What are chromosomes for? The structure and functions of chromosomes. reproduction in the organic world. The structure of germ cells. The history of the discovery of chromosomes

1. The structure of the mitotic chromosome. Types of chromosomes, their number, size. Karyotype and hyogram. human chromosomes. Denver classification of human chromosomes.

In the area of ​​​​the primary constriction, the centromere is located - this is a lamellar structure that has the shape of a disk. It is associated with thin fibrils and the body of the chromosome in the region of the constriction. Usually a chromosome has only 1 centromere, but dicentric and polycentric can occur. Those k-e chromosomes have a secondary constriction, which is usually located near the distal end of the chromosome and separates a small area - a satellite. Secondary constrictions are also called nucleolar organizers, because have on these parts of the chromosomes in the interphase, the formation of nucleoli occurs. The DNA responsible for the synthesis of rRNA is also localized here. The arms of chromosomes terminate in telomeres, the end segments. The length of chromosomes can range from 0.2 to 50 microns. The number of chromosomes in different objects varies considerably, but is typical for the k-th species of animals or plants. The totality of the number, size and morphology of chromosomes is called the karyotype of a given species. Ideograms are pictures or pictures of chromosomes arranged in a row in descending order of size. Such a simple morphological analysis can convincingly show differences in karyotype even in closely related species. The exact number of human chromosomes and the method of their counting in peripheral blood leukocytes was created in 1956. In 1959, an international classification of human chromosomes was adopted, called the Denver classification. According to this classification, all human chromosomes are divided into two unequal groups: 22 pairs of autosomes and a group of heterochromosomes including sex chromosomes (XX and XY). Autosomes are divided into 7 groups according to their size and morphology.

2. Meiosis its biol role, stages. Conjugation xp-m, crossing-over, reduction of the number xp-m. Xp-we are a type of lamp shield. Difference between mitosis and meiosis.

During fertilization, the process of fusion of the nuclei of parental gamete cells necessarily occurs, which should ensure a doubling of the number of DNA and chromosomes in the zygote and, accordingly, in all cells of the developing organism. Consequently, during the formation of germ cells, there must be a mechanism for reducing the number of chromosomes that would compensate for the doubling of their set during fertilization. This is achieved with a special division of maturing germ cells, with reduction division in the process meiosis,- which, in contrast to fertilization, leads to a decrease in the number of chromosomes in the cell by half. It consists of 2 following each other divisions of the nucleus and one doubling of the amount of DNA. Also, there is a recombination of the gene material, an exchange of sections m / y of homologous chromosomes (crossing over), activation of transcription in the prophase of the first division and the absence of the S-phase m / y of the 1st and 2nd divisions. In the body there is a constant alternation of phases, differing in the number of chromosomes per cell. It - haplophase, represented by cells with the smallest number of xp-m, and diplophase. in which cells with a double, 2p the number of xp-m. Depending on the position in the life cycle of the development of organisms, there are 3 types of meiosis: zygotic, gametic, intermediate. Zygous (original) - Meiosis occurs immediately after fertilization, in the zygote. In ascomycetes, sporozoans, and other org-moves, the cat predominates in the life cycle P phase. They can reproduce without sexual reproduction.

Gametic - during the maturation of gametes, in multicellular animals, simple x and some lower plants, prevails 2p phase. R: A green algae that reproduces only through sexual reproduction. Haploid large female and small male gametes, merging, form a zygote, which germinates into a new diploid plant. Later, with the development of the genital organs, gametangia, a reduction division occurs, and haploid gametes are formed. Thus, the haplophase is significantly reduced here.

Intermediate (spore) in higher plants - during sporulation, including the m / y stages of sporophyte and gametophyte. In the organs of reproduction 2p organisms occurs image-e n S (microspores) and $ (megaspores) of germ cells. The difference from the previous type is that after meiosis P cells still divide several times during the reduced haplophase. Har-m for meiosis is that during the prophase of the first division, a special restructuring and arrangement of xp-m occurs in the nuclei of maturing germ cells.

The prophase of the first (I) meiotic division is divided into 5 stages: leptotene - the stage of thin filaments, zygotene - the stage of merging filaments, pachytene - the stage of thick filaments, diplotene - the stage of double filaments, diakinesis - the stage of isolation of double filaments. This is followed by metaphase I of division and subsequent phases of cell division, the next P cycle begins, eventually leading to the appearance of mature reproductive cells. Cells entering meiosis have the usual diploid 2n xp-m number and the amount of DNA corresponding to this number (2c). In the first cycle of meiotic division, a normal S-phase occurs, leading to DNA duplication, i.e. cl contains 4n number of xp-m. In Rust, meiosis is much longer than mitosis in time.

Leptotena- the stage of thin filaments, reminiscent of the early prophase of mitosis, but differs in that during meiosis, the nuclei are larger and the ridges are very thin (so that it is very difficult to trace them along the entire length). In the leptotene, the xp-we are doubled, but the sister chromatids in them cannot always be distinguished, thus.
contains 2n doubled sister chromatids, the total number is 4n due to reduplication in the S-period. A clot of chromatin appears on thin chromosomes - a chromomere, which is strung in the form of beads along the entire length of the chromium. This allows you to make morphological maps xp-m and use for cytogenetic analysis. In leptoten, the process of conjugation of homologous chromosomes, which is important and characteristic of meiosis, begins.

Zygoten- the stage of conjugation of homologous xp-m. At the same time, homologous xp-we (already double after the S-period) approach and form a new xp-mne ensemble, never before encountered in cell division - bivalent. Bivalent are paired compounds of doubled homologous xp-m, i.e. each bivalent consists of 4 chromatids. Thus, the number of bivalents per nucleus will be equal to the haploid number of chromosomes. Unlike mitosis, in the prophase of meiosis, namely at the zygote stage, a small amount of specific DNA, called zDNA, is synthesized. In the mitotic cycle, it is synthesized simultaneously with the bulk of DNA, but during meiosis, it is synthesized only in the zygotenic stage. If you suppress additional DNA synthesis with the help of inhibitors, then chromosome conjugation will stop. The association of homologues most often begins in telomeres and centromeres, the axial strands converge at a distance of about 100 nm, ligaments form between them, and thus the formation of the complete structure of the synaptonemal complex occurs.

3. Pachytene- the stage of thick filaments, called due to the complete conjugation of homologues, prophase xp-we, as it were, increased in thickness. The number of such thick pachytene xp-m is haploid 1n, but they consist of 2 combined homologues, each of which consists of 2 sister chromatids. At this stage, a crossing-over occurs, a mutual exchange of identical sections along the length of homologous xp-m. Here arise different from the original xp-we containing individual
plots that came from their homologues. In pachytene, a small amount of DNA is synthesized (recovery of lost DNA). In the pachytenic stage, the activation of the transcriptional ability of xp-m begins, at this time in $. Amplification of ribosomal genes occurs in germ cells, which leads to the appearance of additional nucleoli. At the same stage, some chromomeres begin to activate and the structure of xp-m changes; they take the form of "lamp shield". These changes are especially visible at the dischuten stage.

4. Diploten - the stage of double threads, the homologues are repelled from each other in the centromere zone, but at the same time, pairs of sister chromatids of each homologous chromosome remain connected m / y in the centromere regions and along the entire length. As the chr-m is repulsed, chiasma is visible in the bivalents of the choir - the place of crossover and adhesion of the chr-m. Only in these areas is the structure of the synaptonemal complex preserved; in divergent areas, it disappears. In the diplomatic stage, the scales take on the form of "lamp shields". These str-ry are found in oocytes and spermatocytes in all animals and plants. On the xp-max of this stage, it is clear that each homologue in the bivalent is surrounded, as it were, by felt, consisting of looped filamentous structures. In this case, the loops are pairwise symmetrical, and each pair departs from a chromomere located on the chromosome axis. This axis is nothing more than two paired sister chromatids, and chromomeres are double sections of condensed chromatin, while loops are decondensed sections of active, functioning chromatin. The loops contain a large amount of RNA, which is synthesized here. According to its characteristics, this RNA belongs to the information one. The loops of these xp-m are formed by a double axial xp-m thread, on which lie multiple transcription points, from which growing RNA molecules depart. The presence of active xp-m in diplotene sharply distinguishes meiosis from mitosis, where, starting from prophase, RNA synthesis completely stops.

5. diakinesis characterized by a decrease in the number of chiasmata, shortening of bivalents, loss of nucleoli. The bivalents take on a more compact form. Xp-we are losing contact with the nuclear envelope. This stage is transitional to the actual cell division. In metaphase I of the division of meiosis, the bivalents line up in the equatorial plane of the spindle

in anaphaseId division, the divergence of the chromatids occurs, but unlike mitosis, it is not the sister chromatids that diverge, but the homologous chromatids, consisting of 2 sister chromatids. During anaphase, allelic genes are consumed in different cells, located in different homologues. The distribution of homologues over cells is completely random, so that there is a mixture, a recombination of xp-m from different pairs.

Following the telophase of division I, a short interphase follows, in which DNA synthesis does not occur and cells proceed to the next division, which does not differ in morphology and sequence from mitotic division: paired sister chromatids connected in centromeric regions go through prophase and metaphase; in anaphase, they separate and diverge one by one into daughter cells. That. during II meiotic division, a cell with 2c count DNA and 2n the number of chromatids, dividing, gives rise to two cells with P content DNA and hrm. P division of meiosis is reduction. As a result of the whole process of meiosis, after 2 divisions, 4 haploid cells are formed from one cell, each of which differs in its genetic constitution.

Differences Between Mitosis and Meiosis:- the presence of active chromosomes in the diplotene sharply distinguishes meiosis from mitosis, where, starting from prophase, RNA synthesis completely stops.

in anaphase 1 of division, chromosomes separate, but unlike mitosis, not sister chromatids diverge, but homologous chromosomes consisting of 2 sister chromatids.

unlike mitosis in the prophase of meiosis, a small amount of a specific protein is synthesized at the zygotenic stage. DNA(z-DNA). During mitotic division, it is synthesized simultaneously with the bulk of DNA.

in plants, meiosis is much longer than mitosis in time. So in Tradescantia, the entire meiosis takes about 5 days, of which 4 days fall on the prophase of 1 division.

during meiosis, in addition to the reduction in the number of chromosomes, a number of other processes occur that distinguish this type of division from mitosis. This is the recombination of genetic material, the exchange between homologous chromosomes (crossing over).

meiosis is characterized by activation of transcription in the prophase of the first division and the absence of an S-phase between divisions 1 and 2.

3. Genetic recombination in prokaryotes. conjugation in bacteria. The sex factor in Escherichia coli, its role. Plasmids, their role in the transfer of genetic information.

Genetic recombination is a general biological phenomenon inherent in all living organisms, from viruses and bacteria to humans. It is based on a complex enzymatic process of interaction of nucleic acid molecules of two parents, leading to the redistribution of genes or their components and, ultimately, to a change in the hereditary properties of the offspring. The great role of genetic recombination as one of the driving forces in the evolution of prokaryotes. The transfer of genetic information in microorganisms occurs through transformation, transduction and conjugation.

Conjugation is the connection of cells of the opposite sex (male f + and female f -) through protoplasmic bridges, through which genetic material is transferred from donor cells to recipient cells within 1.5 hours. Thus, conjugation in bacteria can be considered as an analogy of the sexual process in higher organisms. This process can be conditionally divided into 5 stages: the connection of cells and the formation of a conjugation channel; the connection of homologous sections of chromosomes (synapis) and the formation of a partial zygote; interaction of DNA molecules of parents and formation of recombinant structures; segregation of stable haploid genomes. To establish cell contacts, the presence of special genetic factors, which Luria called ''conjugons'', is necessary. Cell contact is a necessary condition for the subsequent transfer of DNA and sexual recombination.

Sex factor in e.coli (factor f)

For the formation of recombinants, it is necessary to preserve the viability of one of the parents, while the other may die. This made it possible to distinguish between the two sex types f + (donor or male strains) and f - (female strains). Recombinants from crossing f + xf - always belong to the f + type, acquiring

f factor. For such an infectious transfer of factor f into f cells, cell contact (conjugation) is necessary. factor f is DNA in nature, the amount of DNA in factor f is similar to the content of DNA in bacteriophage.

Plasmids are extrachromosomal genetic elements of bacteria. The resistance of cells to the action of various damaging agents, their spontaneous and induced mutability, replication and recombination of chromosomal DNA are controlled by chromosomal and plasmid genes. Bacterial plasmids can carry genes responsible for a variety of host cell traits, including cell growth, RNA, carbohydrate and carbohydrate metabolism, pigment production, and antibiotic production.

4. The first and second laws of Mendel. Cytological substantiation of Mendel's laws. Principles of the hybridological method. Backward and analyzing crosses. incomplete dominance.

hybridological method- 1865 - the basis of genetic analysis, created by Mendel. The essence is the study of the inheritance of individual traits and properties.

Characterized by:

the use of forms of the same species, characterized by a small number of features;

an accurate record of the number of hybrid individuals is kept;

offspring are analyzed individually from each individual.

Depending on the number of signs the crossed individuals differ in, mono-, di-, tri-, polyhybrid crossing is distinguished.

Peculiarities:

obtaining constant forms over several generations, which were later crossed,

analysis of the inheritance of individual pairs of traits in the offspring of crossed plants of the same species differing in one, two, three pairs of contrasting genes, alternative traits (ex: purple and white flowers), in each generation, separate records were kept for each pair of alternative pr-in,

the use of quantitative accounting of hybrid plants that differ in separate pairs of alternative traits in a series of successive generations,

application of individual analysis of the progeny of each hybrid plant.

Monohybrid crossing - parental forms differ in one pair of alternative traits. If the maternal district has purple flowers, the paternal one has white flowers, then the flowers of all f1 hybrid plants turn out to be purple, the white color of the flowers does not appear.

In f1 hybrids, only one of a pair of parental alternative traits develops, the second does not appear, the phenomenon of predominance in the f1 hybrid of a trait of one of the parents Mendel called this dominance. The trait that appears in the hybrid is dominant, and the suppressed trait is recessive. The law of dominance (Mendel's first law) is the law of uniformity, hybrids of the first generation. Hybrids f1 self-pollinated, then in the next generation (f2) plants appear with the characteristics of both parents in a ratio of 3:1. This ratio expresses Mendel's second law, or the law of splitting traits in second-generation hybrids in a ratio of 3:1 in terms of phenotype.

An allele is a different state of the same gene.

Let's say that in the somatic cells of peas there is only one pair of homologous chromosomes, and the alleles that determine the trait of purple color (A) are located in each of these chromosomes in parent plants. Then the somatic cells of a homozygous plant, which have a dominant flower color trait, must carry two dominant AA alleles due to the pairing of homologous chromosomes. Cells of other parental plants with white flowers have recessive aa alleles in the homozygous state. As a result of meiosis, in each gamete there is one chromosome from the pair and one allele - A (dominant) and a (recessive). As a result of fertilization in the hybrid zygote, the pairing of chromosomes is restored, and the formula of the hybrid will be Aa. During the formation of germ cells in a hybrid in meiosis, the chromosomes will disperse into different gametes, and male and female gametes carrying one of the A or a gene allele will be formed in an equal number. During fertilization, male and female gametes of both types will combine with equal probability, resulting in splitting 1 AA: 2Aa: 1aa.

If the F1 hybrid has one dominant of two allelic traits, and in F2 the recessive one is cleaved out in exactly the same pure form as in the original forms, then allele heterozygotes A and a do not mix. As a result, the gametes formed by such a heterozygote are "clean" in the sense that the gamete And "clean" and does not contain from the allele a, gamete and "clean" from BUT. This phenomenon of non-mixing of alleles of a pair of alternative traits in the gametes of a hybrid is called the "law of purity of gametes".

Backcrossing this is a crossing of hybrids with one of the parental forms: such a crossing of an f1 hybrid with a form carrying a given pair of alleles (dominant and recessive) in a homozygous state (recurrent or bicros), and the offspring are designated Fin

When backcrossing the hybrid F1 Ah mixed form homozygous for the dominant allele (ah) all gametes of the parent plant will carry the dominant allele BUT, while F2 hybrids form gametes of 2 types BUT and a. As a result of a random combination of these gametes during fertilization, the offspring is split according to the genotype 2Aa:2AA or 1:1 , phenotypic segregation is not observed

F1 hybrid cross Ah with recessive homozygous (ah) genotype and phenotype 1:1 segregation should be expected. Crossing a form with a dominant trait and a form with a recessive trait is called analyzing cross. Test crosses can be used to test the genotype of an organism of unknown origin. Analyzing cross is a special case of recurrent cross.

Incomplete dominance (intermediate)

In some cases, the trait shows an intermediate expression in heterozygotes when compared with both parental forms. PR: when crossing forms of the night beauty with red and white flowers, the hybrids have pink flowers.

A person has a blood disease - thalonemia, which manifests itself in two forms: large and small. Large is manifested in recessive homozygotes, small in heterozygotes, healthy people are dominant heterozygotes. In the case of incomplete dominance, the splitting by phenotype and genotype coincide and there is no need for analyzing crosses.

5. Genetics of populations of self-pollinators. Selection of self-pollinators. Panmictic populations, their dynamics. Hardy-Weinberg law, the possibilities of its application. Factors limiting the operation of this law.

The equilibrium frequencies of genotypes are the product of the frequencies of the corresponding alleles. If there are two alleles (A and a with frequencies p and q), then the frequencies of the three possible genotypes are expressed (p+q) 2 =p 2 + 2 pq + q 2

This Ur-e in 1908 form. Hardy and Weinberg, according to the formula p 2 + 2 pq + q 2 = 0 , then knowing the frequency of recessive homozygotes, it is possible to calculate the frequencies of all genotypes of the population.

The Hardy-Weinberg problem is never real in its purest form, tk. on the population of deyst-t numerous. f-s that violate its genetic balance. Such processes include mutations, migrations, genetic drift, and eating. and art. selection, waves of life.

Mutations- the only source of genet .. variability, but since they are pr-t with a low frequency, they change the genet. p-py population slowly.

Migrations(gene flow) arise when individuals of one population move to another and interbreed with its representatives. Gene flow does not change allele frequencies in the species as a whole, but in local populations. they change.

Gene drift- change in allele frequencies in a number of generations, caused by chance. reasons, most often the small size of the population.

Waves of life- These are sharp fluctuations in the number of popul, a cat. are periodic in character with different wavelengths or aperiodic, when the wave grows without signs of decay in the near. time.

Eating. selection- the most important factor in evolution. only it determines the adaptive value of the percentage of mutagenesis, migration or gene drift. It determines the diversity of organisms and promotes their adaptation to decay. conv. creatures.

assortative crossing- this is crossing, when the choice of a partner is ok. influence of genotype.

7. Sex genetics. sex chromosomes. Types of chromosomal sex determination. Homo and heterogametic sex. Sex-linked inheritance. Genetic analysis for this type of inheritance.

Sex is a combination of morphological and physiological and physical properties of the body that ensure sexual reproduction, the body's ability to produce sex cells of a certain sign - male and female, the fusion of haploid gametes - fertilized - leads to the formation of a diploid pair, from which a new organism develops.

Sex determination, i.e. switching cells to develop in one case female, and in the other male reproductive organs, in different types carried out at different stages of individual development. The switching mechanism is not fully disclosed. There are the following types of sex determination:

genetic (progamous - the sex of the offspring determines the genotype of the egg; syngomic - the sex is determined at the time of fertilization, depends on the genotype of the sperm)

phenotypic - epigamous, sex is determined after fertilization, under the influence of environmental conditions.

Phenotypic sex determination is a rare thing, since the ratio between the sexes, determined by environmental conditions, turns out to be unstable and undefined. Larvae developing in contact with the trunk turn into males, free into females.

The first data on the relationship of sex with cell chromosomes were obtained in 1902 in the study of meiosis in grass bugs. In males 2n=13 and 2n=14 in females. The study of the course of meiosis showed that in males, the 13th chromosome differs from the rest in larger sizes. The distribution of chromosomes occurred in such a way that half of the cells had (6 + x) chromosomes, and the second had (6 + 0), they had no x chromosome. Obviously, the x-chromosome has deviations in sex determination, since when cells merge (6 + x) (6 + 0) \u003d 13, males develop, while when cells merge (6 + x) (6 + x) \u003d 14, it gives females.

Gametes carrying different sex chromosomes are always formed in equal numbers, this is determined by the mechanism of meiosis. A sex that gives gametes of the same type is called homogeneous. A sex that produces two types of gametes is called heterogeneous. Splitting along it is reminiscent of analyzing crossover. In both cases, the splitting occurs in a ratio of 1: 1, as the statistics show, the splitting by sex really corresponds to this:

Man 51:49

Horse: 52:48

Dog: 56:44

Donkey, sheep: 49:51

Mouse, duck: 50:50

Hereditary sex linkage is the inheritance of traits that controls genes located on the sex chromosomes.

In 1916, the first mutation in fruit flies was discovered - white eyes.

The inheritance of this trait revealed in regular crosses, a dependence was found.

Attention is drawn to the fact that:

receptor cross gives different result, i.e. the direction of the crossing matters.

In F1, only males are white-eyed, i.e. a sign of coupling with a certain sex.

the feature is distributed crosswise, i.e. from mother to son, from father to daughter.

The only recessive allele, neither homozygous nor heterozygous. This condition is called hemizygosity. The trait is determined by a single recessive allele.

Since the distribution of traits clearly repeats the distribution of x-chromosomes, it can be concluded that genes are physically located on chromosomes and are part of them.

Sex-linked in humans, a number of recessive traits are inherited, daltoism, hemophilia, and the absence of γ-globulins in the blood. The lack of organic phosphorus in the blood, the gene for darkening of tooth enamel, is inherited dominantly sex-linked.

Hereditary linkage to the Y chromosome, from father to son. Signs of syndactyly, hypertrichosis of the body.

Inheritance in female heterogeneity.

This type of inheritance has been noted in chickens, butterflies, and some fish. The color of the feather in chickens, the color gene is sex-linked.

R W:XY x M:XX

striped black

plymutrop australorp

F 1 M:XX W:XY

Striped Black

R W:XY x M:XX

black striped

F 1 w:XX m:XY

striped striped

Reciprocal crosses give different results

Criss-cross inheritance

The recessive gene appears in the hemizygous

Sex-limited traits, which appear only in one sex due to the analytical structure, although the genes that control the trait are present in both sexes, for example, milk-fat cows, egg-laying chickens, etc.

Sex-dependent traits, such as the development of horns in sheep. Heterozygous rams (Hh) are horned, i.e. their horn is dominant, and heterozygous sheep (Hh) are hornless, i.e. horniness is recessive. According to this principle, many secondary sexual characteristics are inherited.

8. Linkage of genes. Clutch groups. Genetic analysis of gene linkage. Linkage and decussation in Morgan's experiments with Drosophila.

The number of chromosomes in different species is small compared to the number of genes. Drosophila has more than a thousand genes on 4 pairs of chromosomes. If the genes are on chromosomes, then each of them must carry a whole group of genes. These genes, combined on the same chromosome, cannot obey the rule of independent inheritance. Morgan showed that genes located on the same chromosome form a single linkage group.

A dihybrid cross was carried out on Drosophila, in which the inheritance of the following traits was studied:

R gray body x black body

rudimentary cr. kr norms

F1 1) gray body 2) black body

norms. rudimentary wings. cr.

3) gray body 4) black body

conceived. cr. norms. cr.

Analyzing crossing showed that the hybrid forms only two types of gametes, in which the combination of genes has not changed and remains the same as in the parent individuals. This inheritance has been called linked.

Analyzing cross is delivered in two directions. For backcrossing, a female hybrid was selected from among the hybrids and crossed with males - the lines of the analyzer.

A hybrid of the fetotypic class appeared in the crossing, which indicates the formation of 4 classes of gametes in the hybrid female. But instead of equality of classes, as in dihybrid crossing, descendants appeared with combinations of traits characteristic of parental forms - 83%, i.e. gene linkage is observed in 17% of cases.

Morgan suggested that the decoupling of genes or recombination occurred due to crossover - crossing over in hybrid females. Drosophila males and silkworm females do not have crossing over, they have absolute gene linkage.

Gametes with chromosomes that have undergone crossing over are called crossover, individuals with new combinations of traits that have arisen as a result of the fusion of crossover gametes are crossovers or recombinants. Crossover classes are the result of the mutual exchange of chromosome members, so they always appear in pairs and are numerically equal to each other. The crossover frequency is defined as the ratio of the number of crossovers to the total number of offspring in the analyzing cross and is expressed as a percentage. 1% decussation is a unit of distance between gametes and is called a morganide. This frequency is different. The combination of genes is permanent. This suggests that the genes occupy a permanent place in the chromosome, the location of the genes in the chromosome is linear, the frequency of crossing over reflects the distance between the genes: the closer the genes are located on the chromosome, the less the probability of crossing over (the higher the strength of gene adhesion). The farther the genes are from each other, the more likely the crossing-over (less cohesive force).

9. Polyploidy. Autopolyploidy, its phenotypic effects and genetics. Amphidiploidy as a mechanism for obtaining fertile allopolyploids. The value of polyploidy in evolution and plant breeding.

Genomic mutations are mutations affecting the number of chromosomes that change the genome-haploid set of chromosomes with local genes in them. These include aneuploidy and polyploidy.

Polyploidy is a change in the number of chromosomes, a multiple of the haploid.

Multiplication of the same haploid number of chromosomes (genome) is called autopolyploidy.(AAA, AAAA, etc.) Combining several different genomes during hybridization called allopolyploidy(ААВ, ААВВ, АВВ, etc.) Distinguish between balanced polyploidy, with an even number of sets of chromosomes, and imbalanced, with an odd number.

Polyploidy is rarely found in living things, but is common in plants. In the living, polyploidy is known in hermaphrodites. (earthworm)

A number of events lead to the appearance of polyploidy:

1) With non-separation of chromosomes in meiosis, the gamete can receive a complete somatic set of chromosomes;

2) Polyploids can arise from spontaneous duplication of chromosomes in the somatic cells of the meristem. This leads to the emergence of tetraploid shoots, the flowers of which will produce diploid gametes.

Polyploidy can be induced artificially by exposing the plant to the action of substances that affect the formation of the division spindle.

The polyploid phenotype is characterized by a number of features:

Gigantism (with a high degree of polyploidy, dwarfism is possible);

Low osmotic pressure.

Autopolyploidy. Autopolyploids are characterized by sterility.

The genetics of autopolyploids is characterized by 2 main features:

It is difficult to split recessives;

The law of purity of gametes does not apply to polyploids.

In natural populations, many polyploids are of a hybrid nature and are allopolyploids. Emerging amphihaploids(AB) are sterile and are eliminated from the population.

Experimental pathway for the emergence of fertile amphidiploids

(allotetraploids) was shown by G.D. Karpechenko. He managed to get a fertile hybrid between radish and cabbage.

10. Mutation theory. Class-I mut-th according to the character of the change in the genotype. Quantitative methods for accounting for mutations (cib, Meller-5).

A mutation is a change in hereditary material. The mutation theory originated in 1901 - 1903, it was created by Hugo de Vries.

Basic provisions: 1) Mutations occur suddenly, abruptly as discrete changes in traits. 2) The resulting mutation is stable and is inherited. 3) The process of occurrence of mutations is an undirected process. The same mutation can occur repeatedly, along with beneficial mutations, and harmful mutations. 4) Mutations are qualitative changes. They do not form continuous series, they are not grouped around the average.

Types. The classification of mutations can be based on different principles. Accordingly, mutations can be classified in various ways.

generative mutations affect the genes in the cells involved in reproduction, and therefore appear in the offspring, are inherited. The number of emerging mutant cells will depend on the stage of their formation at which the mutation occurred. With its early appearance, for example, at the stage of mitosis preceding meiosis, a bunch of mutant cells may appear. If the mutation affected the cell at the final stage of its development, it will be single.

Somatic mutations are the cause of the appearance of clones of genetically different cells - mosaicism. In sexually reproducing organisms, where generative cells separate early, somatic mutation can produce a clone of cells with a mutant trait that can be artificially propagated vegetatively. In addition, a mutation that affects the cells of the meristem, from which the shoot with flowers is formed, can become generative. Kidney mutation.

The most clear is the classification of mutations according to the nature of the changes in the genotype. These are mutations nuclear affecting the main array of the genotype and mutations plasma, affecting the genes of cytoplasmic organelles (mitochondria, plastids).

Nuclear, depending on the scale of damage, are divided into: genetic, changes affect the structure of individual genes (transition - the replacement of one purine with another purine or pyrimidine with another pyrimidine; transversions - the replacement of a purine with a pyrimidine or vice versa), chromosomal mutations or chromosomal rearrangements that affect the structure of chromosomes ( Deletion- part of a chromosome is missing duplication- one region of the chromosome is present more than once, Inversion-in one of the sections of the chromosome, the genes are located in reverse order compared to normal. If a segment of the chromosome includes the centromere, the inversion is called pericentric, if this segment is inside the arm and does not affect the centromere, it is called paracentric, Translocation- exchange of segments of non-homologous chromosomes), genomic mutations that change the number of chromosomes (changes expressed in aneuploidy - a change in the number of xp-m, not a multiple of haploid, or in polyploidy - a change in the number of xp-m, a multiple of haploid: autopolyploidy - an increase in the number of xp-m sets and allopolyploidy - a doubling of the number xp-m in a sterile hybrid).

In 1927 Meller developed a quick and easy way to detect sex-linked lethal mutations in the chromosome as a whole. A special line of Drosophila was created for this method. Its feature is that the X chromosome contains two inversions. The first is very large, capturing most of the X chromosome (sc 8), the second is smaller and is located inside the first. These two inversions lock the crossover. The females are homozygous. X chromosomes are also labeled with the apricot gene (w a) - apricot eyes and yellow-yellow body.

Homozygous females are bred with wild-type males whose sperm are examined for the presence of recessive lethal mutations. Daughters from such a crossing have one Meller-5 chromosome and one chromosome under study, each of the F 1 females is crossed individually in a separate test tube with the F 1 male, which has a single Meller-5 type x-chromosome. The appearance of wild-type males in F 2 indicates that in the test tube there is not a single recessive lethal mutation. The absence of wild-type males in F 2 indicates that the investigated chromosome contains at least one newly emerged lethal mutation. Moller showed that the frequency of mutations increases sharply under X-ray irradiation and the action of the poisonous substance mustard gas.

Significance: in many cases, xp-nye and gene mutations are lethal. As a result, some xp mutth def. genes can be together, and their total. the effect can lead to the appearance of a "favorable" trait. Gene mut. can lead to the emergence of th in opred. locus of several alleles. This increases the heterozygosity of the population and its gene pool, and leads to an increase in intrapopulation variability.

11. Methods for studying human genetics. Hereditary diseases, their distribution in the human population. Chromosomal diseases. The use of biochemical methods for the diagnosis of hereditary diseases. Cell cultures.

The biological species Homo sapiens is part of the biosphere and the product of its evolution. A person obeys the laws of hereditary variability. We are something other than a product of our genes. Human genetics is the science of his heredity and variability. There are 3 main areas in human genetics:

the problem of genetic individuality and its influence on the formation of a person's personality, the development of inclinations and abilities, the individuality of reactions to external influences.

the work of genes in the body in the process of individual development and life.

genetics of hereditary diseases, adjacent to medical genetics.

Methods for studying human genetics.

1. Pedigree or genealogical method.

Galton introduced the analysis of pedigrees into genetics, proposed a method for recording them and obtained interesting results; in the analysis of pedigrees used statistical methods.

Further, Galton and his student Pearson developed this direction and created biometric genetics. Pedigree analysis allows you to establish the type of inheritance of a trait in humans. Depending on inheritance, pedigrees have a different look. With dominant autosomal inheritance, the trait manifests itself phenotypically in each generation in all heterozygotes and does not depend from sex. Pedigrees in recessive inheritance differ in that the trait may be absent in several generations, and its manifestation is accompanied by related marriages. There are 3 degrees of relationship:

parents, children, brothers and sisters. 50% common genes.

uncles, aunts, nephews, nieces. 25% of common genes.

cousin marriages. 12.5% ​​of common genes.

Pedigrees in sex-linked recessive inheritance are characterized by well-traced criss-cross inheritance, and by the fact that the trait appears in males.

2. twin method,

Showed that twin samples were statistically acceptable, this made it possible to study the genetics of normal variability.

developed a reliable method for diagnosing twins using a large number of criteria.

proposed to study both monozygotic and dizygotic pairs of twins, bearing in mind that RBs are born at the same time and develop under the same conditions.

All properties of an organism ARE DETERMINED BY THE INTERACTION OF 2 FACTORS - the genotype and the environment. By studying rb and rb, it is possible to identify the influence of the genotype and environment on the development of traits. rb and rb are compared for a number of signs in a large sample. Based on the data obtained, concordance indicators (frequency of similarity) and discordance are calculated (frequency of differences). These indicators can be used to assess the significance of the genetic component in a given disease. They also allow you to establish under what conditions this or that symptom manifests itself.

The frequency of twins is different in different populations.

3. Cytological method

The basis is knowledge of human chromosomes in the norm and analysis of deviations from it. According to the Denver classification, all human chromosomes are divided into 2 unequal groups: 22 pairs of autosomes and 1 group of heterochromosomes, including sex chromosomes (xx, xy). A new the concept of chromosomal diseases, the cause of which is a violation of the number and structure of chromosomes. The mechanism of this phenomenon is a violation of meiosis, which is expressed in non-disjunction of chromosomes. This leads to trisomy and monosomy of zygotes. The reasons for non-disjunctions are the same as the causes of other mutations: ionizing radiation, exposure chemicals,alcohol,pollution.

There are 3 types of chromosomal disorders in humans, which are associated:

with an excess of genetic material (olisomy, polyploidy, duplication, triploidy).

with the loss of part of the genetic material (nullosomy, monosomy, deletion).

with rearrangement of chromosomes (translocation).

Violations associated with an excess of chromosomal material are possible both in the autosome system and in the sex chromosome system. In the sex chromosome system, trisomy on the x chromosome (triplo-x syndrome), Klinefelter syndrome with various variants are known.

Trisomy on the x-chromosome in women causes mental retardation (mild oligophrenia), dysfunction of the gonads.

Klinefelter syndrome exists in several variants that differ in the genome of excess x and y chromosomes. Variants 2-4x + 1y, 1x + 2-3y, 2x + 2y are known. Men with this syndrome are characterized by high growth, they are characterized by eunuchoidism, the development of secondary sexual signs of the female type, complete sterility, mental retardation.

Diagnosis-analysis of karyotype + barr bodies.

A common chromosomal disease is Down syndrome or trisomy on chromosome 21.

Characteristics: well-defined diagnostic features; frequency of the syndrome increases with maternal age; males are infertile; life expectancy is shortened; risk of death from leukemia is 20 times higher.

Trisomy on the chromosome group d (13-15) or Patau syndrome and trisomy on the chromosome group e (16-18), Edwards syndrome is less common. These chromosomal anomalies cause severe and complex malformations, the life expectancy of infants is estimated at several months.

Shershevsky-Turner syndrome-monosomy on the x-chromosome (x0). Growth retardation, sexual development, underdevelopment of internal organs, defects in the cardiovascular and musculoskeletal systems, short stature, a peculiar head position (sphinx head) and pterygoid folds on the neck.

4. Biochemical method.

gene research

at the level of cellular structures

Hereditary metabolic diseases are diagnosed.

For research, short-moving cell cultures are used - these are cultures of lymphocytes, as well as long-moving cultures of fibroblasts.

Prenatal diagnosis - uses the method of chromosome analysis, and biochemical. For this, amniocentesis and chorion biopsy are used. During amniocentesis, amniotic fluid is analyzed, a sample of which is taken through the abdominal wall at 14-16 weeks of gestation. Living cells are separated by centrifugation and cultured. Allows you to set the sex the child and the degree of risk for sex-linked diseases.

Chorionic biopsy, when taken to study the villi of the outer germinal membrane at 8-10 weeks of gestation, allows you to establish biochemical and chromosomal disorders without cell cultivation.

5. Population method.

The answer to the question of how Mendel's laws are implemented at the population level, how factors such as mutations, selection, migration, genetic drift affect its structure. This is necessary for understanding the epidemiology of hereditary diseases, planning activities that can prevent adverse effects on the genetic human apparatus. Research can be divided into 2 groups:

1-descriptions of populations and their genetic composition

2-analysis of the causes of changes in the gene pool.

12. The origin of life on earth. The development of ideas about the originlife. The main stages of chemical and biol evolution.

This problem is one of the central problems of natural science. There are several approaches to the concept of "life":

substrate - life is determined through the structure of the substrate (proteins, nucleic acids and phosphorus - organic compounds)

functional - through functional manifestations, open self-reproducing systems

substr-functional approach - living organisms are open self-organized and self-reproducing systems consisting of proteins, nucleic acids and organophosphorus compounds.

The development of ideas about the origin and life:

1) creationistic pre-I - about deities, the creation of the world (all living beings were created by God, then their evolution followed (as scientists of that time thought).

spontaneous, the origin of life - was common in China, Egypt, Babylon. An alternative to creationism. Received distribution. in the 16th century Fish - from silt, mice - from mud (Paracelsus, Copernicus, Goethe).

panspermia hypothesis - ideas about the possibility of transferring life in outer space from one cosmic body to another. Life originated from space. embryos simple organisms hit the ground along with dust and meteorites. Supporters - Louis Pasteur, Richard.

4) origin. living from non-living. Life arose on the basis of the general laws of nature. There was not a large material system, which had a high density and a huge temperature, consisted of particles-quarks and leptons. The system disintegrated due to a violation of gravity. stability, there was an explosion and 15-20 billion years ago - the beginning of the universe. In the far the Earth arises and in the rez-those chem. evolution creates life. Ex-t also tz. that the Earth has a cold origin (Otto Schmidt). The Earth was formed from a protoplanetary cloud with a low temperature. This cloud consisted of gas, dust and many particles.

5) Buddhist version - life was created by the world mind. This approach was not satisfactory.

Conditions for the emergence of life:

1) the presence of a certain chem. elements - 21 elements, the most important are C, 02, S, P, H, N. As a result of chemical evolution, a sample of the compound is C 4+. It has a unique, holy mi: it forms a connection with conjugated bonds (1 and = 2 bonds). This leads to increased stability Comm-I and chem. act-ti.

The presence of external sources E(UV, electrical discharges, heat, radioactive radiation).

The absence of free 02. As a result, the processes of synthesis prevail, and not the decay of org mol.

4) Withdrawal of synthesis compounds from the synthesis zone, because at the stage of abiogenic syntheses, the role of non-equilibrium products is manifested.

The emergence of self-organizing systems. There were coacervate drops with unequal. internal structure, they had an oral exchange of in-in. Prebiol selection was subjected not to certain proteins, but to protobionts (the first living organisms). Microspheres with d = 2 microns were the first self-organizing s-mi. Inside were proteinoids. Engein - the first were hypercycles. From them - hypercycles of the 2nd order. According to Engein, prebiol. selection among hypercycles led to their improvement - as a result, the first self-org. systems.

The emergence of the gene. code and appearance of lipid membranes.

appearance of coenzymes

The emergence of life: the first living org-we were heterotrophs. Life existed in the form of simple multi-species systems with food chains. The first org-we arose in the form of a set of individuals in the primary. biogeocenosis. The most ancient org-we were in the Archean (3.8-4 billion years ago) - prokaryotes. They exist in the environment, using ready-made org. in-va, the cat in the ocean was getting smaller. At this time, the first autotrophs appeared. They were able to synthesize org in-va from inorg, using the energy of chemical bonds or the sun (a prerequisite for the emergence of chemo- and f / synthesis). The first f / synthetics appeared. about 3.5 billion years ago Their predecessors are anaerobic, bact. They formed stromatolites (layered calcareous formations in the form of pillars from the remnants of bacterium and cinnamon algae). There was an increase in 02 in the atmosphere, this led to the appearance of eukaryotes. The first eukaryotes arose 1.5 million years ago. n. Steel is numerous, about 1 million years ago. I'm sorry, anaerobe, eukaryotes - flagellum-e rast. and water. Simple and complex multi-organizations arose. Primitive plants and living things appeared 650 million years ago. Modern living things have risen in the Cenozoic (65 million years ago). Further evolution led to the rise of people. In the crust, time, there are 3 n / kingdoms: archeobact, eubact and eukaryotes.

Archeobact. live in silt, in volcanic. sources. dominated by early stages development of life on earth. They were the first prokaryotes. Origin eukaryotes: noun 2 hypotheses - invagination and symbiotic th. Intussusception: cells had a double membrane, they could form invaginations and other cells were captured. Symbiote-I: several types of heterotrophs arose from the primitive cl. and autotroph. cl, when they were combined, a new organism arose. Those. chloroplasts were f/synth bacteria, and mitochondria were heterotrophs. anaerobe. bacteria.

The main stages of biopoiesis (chemical and biol. evolution):

1) education biol. monomers. The atmosphere of the Earth at first wore a recovering character. There was no freedom. 02, but there were vapors of H20, CH4, NH3, CO and CO2. In the results of those chem. reactions rise-whether org-e compounds: HSON, HCOOH, etc. These compounds-I react with each other. There are biopolymers - a/c and nucleotides. Those. synthesis org. compounds went in the early stages of the evolution of the sun. systems. A / c, Porphyria, pyrimidine, purine were found in meteorites. The monomers were linked together by phosphorus bonds.

2) the formation of polymers, i.e. the formation of ether bonds. There was a combination of simple substances into polysaccharides, peptides, etc. They were concentrated in the waters of the primary ocean.

3) arr-e self-organizing systems, i.e. protobionts emerged. Oparin suggested that these are coacervant drops of genes that control morphogenesis. Evol. role - gene mobile retrovirus-like elements can cause large mutations.

13. Genetic theory of natural selection. Object, sphere, action and mechanism of selection, its quantitative characteristics. Factors affecting the efficiency of selection.

Natural selection is the most important driving factor in evolution, which determines the directed change in the composition of the population, i.e. adapting them to environmental conditions. Darwin emphasized that natural selection is selection that occurs in nature without human intervention. This is conservation and preferential reproduction. The experience of the fittest. Selection occurs as a result of the struggle for existence through elimination, therefore phenotypes are selected. Living organisms compete. Selection is based on phenotypes, but genotypes are selected. Moreover, not individual genes are selected, but integral genotypes that determine the ontogeny of the next generation.

Newly occurring mutations reduce fitness. The selection is based on combinative variability - the main material for selection. Phenotypic expression of mutations, i.e. the degree and nature of the change in the organism depends both on the genotype and on the environmental conditions in which this genotype is realized. Mutational variability is not directed, but combinative variability can be considered random only in the presence of panmixia, i.e. accidental crossing of individuals of a given generation. However, since only sufficiently adapted individuals reproduce and this occurs from generation to generation, in a series of generations, the combination-directed process, even in the case of panmixia.

A complex hierarchical system of intraspecific groupings is optimal for evolution, because it provides rapid identification of new alleles, rapid spread of adaptive variants, and a high level of variability. The evolutionary process is influenced by population fluctuations: with an increase in population, a large number of combinations are realized, which ensures an increased genetic diversity of the population. With a decline in numbers, unfavorable variants are eliminated and homozygosity for unfavorable ones increases.

Natural selection is a directed, vectorized process and, like any vector, it has 3 parameters: the application point, i.e. the sign according to which selection takes place; the value characterizing the adaptive value, or relative fitness; the direction determined by the condition of the struggle for existence.

15. View as a stage and result of evolution. Definition of the concept of view. View in prokaryotes and eukaryotes. Polytypic and monotypic species.

The concept of species is based on: systematics, genetics, ev. theory.

Eidology is a science of study. kinds. View - (logical meaning) - an expression of similarity for a number of single parameters. In history, many concepts of understanding the species have been created.

The first Aristotle is a group of similar organisms. J. Rein - these are small aggregates of organisms that reproduce their own kind. Linnaeus - as a system category for classification (the main criterion is morphological similarity), it was proposed to compare an individual with museum specimens - a typological concept. There was a nominalistic concept - pitchfork is abstract. The polytypic concept consists of 2 or more subspecies. Monotypic - does not divide into subspecies. Tinkofka warbler - European, Siberian, Altai. Modern - Biological concept - (Mair, Dovzhansky, Zavadsky, Timofeev-Resovsky).

reproductive unit - that is, individuals of a given species interbreed with each other and are reproductively isolated from representatives of other species.

ecological unit - each species im. your eq. a niche population of one ecologically replaceable.

genetic unit. general gene pool, in which each individual named after them. Small. plot.

View is a group of actually (or potentially) interbreeding populations reproductively isolated from populations of other species. The basis is the ability to interbreed.

But it is not applicable for individuals with asexual reproduction for paleontological.

View real because comes from the original population, which has a gene pool inherited from the ancestors and which determines further development, they are ecologically replaceable, i.e. have a common ecological niche.

View criteria- is a set of certain signs, a cat. allow you to define a species, to separate it from other species - which determines the place of species in the general system of organs. peace.

Main criteria . Morphological- the similarity of the external and internal structure of individuals. (but sexual deformism, twin species (they are outwardly similar, but they are not genetically isolated) common vole 1c.–5p.c.

Genetic - species is a genetically closed system. They do not cross each other.

Ecological- own ecol. niche (living space and food resources.) it can be potential and real.

Geographical- occupies a certain area - a historically established area of ​​​​distribution, where the species occurs throughout its life. It can be continuous, dejunctive (broken) depending on the size of the range - Cosmopolitans, Endemics, Relics, Substitutes.

Physiological- the similarity of the life processes of individuals of the 1st species is the reason for reproductive isolation.

Additional:

1) karyological - the structure and number of chromosomes.,

2) B\x - difference in the composition of proteins of alkaloids, glycosides.

3) the criterion of nucleotide specificity - the ratio of T + C to A + T determines the coefficient.

4) molecular hybridization - DNA is isolated from two species. Unwind and 1 chain. Cool and watch how the formation of duplexes goes (speed).

5) immunological - according to the reaction of sediment formation, they judge the relationship of species.

6) ethological - similarity of behavioral response .

7) palynological - analysis of spores, pollen grains.

8) albumin index - serum protein in which groups of organisms differ greatly.

9) heat resistance of cells and tissues (in voles). But to describe the view, an integrated approach is needed.

View structure. The question of a structural unit has not been resolved, since it is complex and there are many transitional forms.

half view- an ecological or geographical race almost attained the position of an independent species. This is a group of individuals within a species, which is almost isolated from other individuals. crossing almost never occurs.

Subspecies- a group of morphologically similar individuals, occupying a certain part of the species range and phenotypically different from other similar groups i.e. - by external Diagnostic features - occupy isolated areas, are part of larger structural formations. Common fox - 20 subspecies.

ecological race- ecotype - a group of individuals that is well adapted to local conditions of existence. (ant - forest, meadow, in plants on the south. And north. Slopes).

population a group of individuals united by the unity of life activity within a population.

In animals within a population - race, tribe, aberration - excellent, according to morphologist. and physiologist.

The more structured a species is, the more evolutionarily advantageous it is. And this is evidence of speciation.

View - a group of individuals similar in morph. And genetic traits, occupying a certain area, and able to interbreed with others.

But for agamic species - agamos - celibacy, species breeding without fertilization, - parthenogenetic- parthenos - virgin - the female germ cell develops without fertilization, - self-fertile. – for them kind- a group of phenotypically similar individuals with a closely related genotype, and related by a common evolutionary fate - there is no genetic combinatorics.

Kind of controversial concept as a step in the evolutionary process, then it is impossible to select all the criteria for it, some are blurred or as a result of evolution– all criteria are shown very brightly.

16. Speciation is the source of diversity in wildlife. Mechanisms of allopatric and sympatric speciation.

Speciation - proc. the emergence of one or several new species from species that existed earlier.

Speciation is the main stage of the evolutionary process. With the formation of new species, the transition of quantitative changes into qualitative ones. Distinguish between gradual and instantaneous. The gradual is divided into allopatric and sympatric.

A necessary condition for any speciation is reproductive isolation. Significance - it contributes to the differentiation of forms and their adaptations to various environmental conditions.

allopatric– formation of new species on the basis of spatial isolation. It was discovered by Wagner. In the 20s. contributed Zavadsky, Mayer, Clausen,

Populations fall into different environmental conditions. Through differentiation and isolation, one evolving group breaks up into 2 or more evolving units. Complete reproductive isolation has not yet been established between populations. Populations become so genetically different that they lose the ability to interbreed. New species are emerging.

It can happen in two ways:

1) When there is an expansion of the range of the original species. When settling, populations adapt to new conditions.

2) New species can arise through fragmentation (disintegration of the range of the parent species). Populations are so isolated that gene exchange is impossible.

Adaptation to new conditions and random gene drift in a small amount. pop-x lead to changes in the frequency of alleles and genotypes. As a result of the long separation of the pop-th m-they may have a genetic. isolation that will remain even if they are together again.

Example: May lily of the valley.

It is not always mere isolation that leads to speciation. More conditions needed:

1) Elimination of gene flow, resulting in differences between populations of the species.

2) The rate of change in the environment does not exceed the rate of compensatory adaptations.

3) New environmental conditions must be maintained for a long time.

sympatric. A new species arises within the range of the original species. Nebh-mo development k.-l. fur-ma reproductive isolation. The following methods are known.

1) The emergence of new species by changing the karyotype, for example, with autopolyploidy. Groups of closely related species with multiple numbers of chromosomes are known. Chrysanthemums have a multiple of 9, 18, 27, etc. Polyploidization processes are reproduced by delaying chromosome segregation in meiosis. Polyploids can occur naturally. The resulting polyploid individuals can produce viable offspring only when crossed with individuals carrying the same number of chromosomes.

Within a few generations, if the polyploids pass the "control" of natural selection and turn out to be better than the original diploid, they can spread and coexist with the species that cobred them, or, more often, simply displace it.

Among animals, polyploidy plays a lesser role in speciation.

2) By hybridization with subsequent doubling of the number of chromosomes - allopolyploidy.

3) Seasonal isolation. Terms of color-I come-Xia for different. time. Pinus radiata flowers in February and P.attenuata in April.

4) Environmental isolation. Two species, inhabited in the same region, prefer different. conditionally inhabited. Viola arvensis grows on calcareous soils, while V.tricolor grows on acidic soils.

5) Mechanical isolation. Closely related species of plant pollination are different. animals.

6) Non-viability of hybrids, sterility of hybrids in F1, inferiority of hybrids in F2.

Features of sympatric speciation - the emergence of new species, morphologically close to the original.

50% of plants are allopolyploids (cultural plum 2n = 48 arose by hybridization of blackthorn 2n = 32 with cherry plum 2n = 16).

18. Basic forms of natural selection. Examples and results of their action. The role of selection in evolution.

Schmalhausen contributed to the development. He put forward ideas about stabilizing and driving selections. Another destructive, destabilizing, frequency-dependent, K- and R-selection.

1. Stabilizing - if the environmental conditions are relatively constant, it contributes to the elimination of individuals with deviations from the average value of the trait and property, i.e. which deviate markedly from the norm.

A) Normalizing - leads to the elimination of deviations from the norms. The result is the creation of a coherent functioning genome. Stab. culls - poorly adaptive gene. Variants to external factors. – gene variants that are characterized by a decrease in fertility.

Example: the established sizes and shapes of flowers in insect-pollinated plants, they correspond to the structure and shape of the body of an insect - pollinator.

B) Canalizing - means the survival of organisms with a more stable mechanism of ontogenesis. As a result, the developmental processes of the organism are stabilized. The lobe-finned fish, tuatara, and gingo have survived. Hensley called this constancy - persistence - that is, evolution without change. Mutations accumulate during autoregulatory development. They remain in a heterozygous state, thereby creating a mobilization fund of variability. That. occurs - autonomization - less dependence of development on external factors. PR: photoperiodism of plants - they respond to changes in the photoperiod, they do not respond to external factors.

2. Driving - manifests itself in regularly changing environmental conditions, individuals with deviations from the average value only in one direction are preserved, it is not favorable for representatives of the average norm.

A) directed - acts when there is a slow change in the environment and there is a gradual transformation of the population. Or with a fast one, it also goes faster. Ex: the emergence of insect resistance to pesticides. They develop resistance. The mechanisms are not the same. In some cases, it is determined by the dominant gene, in others it is recessive. Ex: the development of immunity to the oyster virus. As a result, 10% of the population remained. However, gradually the number began to recover. And for 25 years it has become more than the original. Resistant individuals bred.

B) Transitive - its action can be traced to the example of the study of industrial melanism. The light color of butterflies made them invisible at night on tree trunks. After darkening, they gradually became dark in color, because. light ones were exterminated by predators. Under conditions of pollution, both light and dark forms were produced, mainly dark forms were obtained. It turned out that they are genetically different.

Difference from directed - starts from the original forms.

3. Disruptive - tearing - favors the preservation of individuals with an extreme expression of signs and eliminates intermediate forms. Ex: oceanic islands and the presence of insects on them, either with strong or without wings.

4. Destabilizing - aimed at increased volatility. under different environmental conditions.

5. Frequency-dependent - depends on the frequency of occurrence of genes. In favor of rare genotypes. Ex: The ratio of simulators and models of insects. The more imitators, the more inefficient selection. Migrants get an advantage when crossing as representatives of rare genotypes.

6. K- and R- there are two approaches to the reproduction of species. Producing a large number of eggs. They use little energy in the body. And vice versa. K- and R - strategy. K - favors slower development, greater competitiveness, late reproduction, larger body sizes, does not a large number descendants.

R - favors rapid development, maximum population growth rate, early reproduction, small body size, a large number of small offspring.

R - more individuals, K - ability is more effective. Use of environment resources.

In nature, they appear together. Ex: Tropical ants first R-strategy - the capture of new territories, colonization, after saturation of the range, the direction of selection changes. Intraspecific competition is escalating. And there is K-selection (Oyster - 500 million per year, chimpanzee - 1 child in 5 years).

7. Sexual - refers to the signs of individuals of the same sex. The result of an adaptation that ensures the success of individuals in leaving behind offspring. Ex: bright color male. (tournament combat weapon, etc.)

The role of natural selection. The pressure of selection can lead to certain results only within the framework of the governing physical and chemical laws. The nature and function of animals are ultimately limited by the fundamental properties of the elements and molecules of which they are composed. 1 - Supportive. - a certain level of fitness, allowing it to exist in given conditions. 2 - accumulative - selection preserves deviations increasing adaptability. They accumulate in the population. The phenotypic expression of traits is enhanced. Selection for a given trait acts in one direction, then the trait is enhanced. 3 - The creative role is manifested - it changes the phenotypic expression of the mutation, creates gene complexes that ensure the adaptability of the next generations;

promotes the formation of new species;

there is a process of adaptation of organs to environmental conditions. Wed and coexistence with other organisms; - to autonomization of development from external factors; - to progressive evolution, determining the pace of evolutionary transformations.

It is a self-regulating process. Analogy with an automatically adjustable device. Regulator, object, direct and feedback channels. As a regulator - the external environment (biogeocenosis), controlled object - population, direct connection - to the population, reverse - from the population to the biogeocenosis.

Self-regulation scheme

19. Isolation as one of the factors of evolution. geographic isolation. Biological isolation carried out by pre- and post-zygotic mechanisms. The role of isolation in speciation.

Insulation is a necessary factor as speciation process is impossible.

2. Biological. prezygotic mechanism - before the meeting of gametes in animals, and before gametophytes in plants 4 forms.

2) seasonal, 3) behavioral, 4) mechanical.

1) biotopic. - by habitat, i.e. species found in 1 geographical area, but occupies different biotopes. Pr: in northern Am. - 3 in. oak (sandy, calcareous, igneous).

2) seasonal - when a species lives in 1 geographical area, but differs in terms of reproduction. Ex: c. Drosophila. - breed day and night.

3) behavioral - different types of animals have features that do not allow the cat to enter into breeding with representatives of another species. There can be different mechanisms - visual, - hearing, - smell, - touch.

Pr: Am. Firefly - sees - light signals (in different species - yellow, green. blue.)

4) mechanical - the difference in the size and morphology of the genital organs in both animals and plants (flowers under certain insects).

Postzygotic 1) the death of gametes - there is insemination, but the egg is not fertilized.

2) the death of zygotes - there is fertilization, but it dies due to the immunological incompatibility of gametes and tissues.

3) the death of hybrids - the organism is not viable. 4) Formation of styryl descendants.

Each species is a genetic system in the course of evolution. More efficient prezygotic mechanisms. Factors that enhance the genetic difference between species, i.e. each species is separate from other species.

The isolation is non-directional and stochastic.

20. Gene drift and population waves as factors of evolution, their role.

Genetic drift is a change in the frequency of genes and genotypes in small populations, which occurs under the influence of random factors. The phenomenon was discovered by Sewelm Wright and Ronald Fisher, in Russia by Dubinin and Romashov. The occurrence of genotypes in a population depends on 4 factors.

population size

Wright found that in a small population, genetic drift is very efficient. It prevails over the action of selection - in a large population, selection prevails.

mutation pressure

High mutation pressure (high mutation rate) prevents gene drift from acting.

gene flow

For gene drift to be effective, a population must be isolated from neighboring populations. Even a small amount of gene flow weakens the effects of genetic drift.

allele selective value

The higher the selective value of the allele, the higher its advantage in selection, the lower the genetic drift.

Thus, genetic drift is effective when

if the population is represented by small isolated colonies;

if the population is large but subdivided into small groups of micropopulations, the cat is also isolated from each other

if the population is large, but periodically its number drops sharply and the population reappears at the 1st stage of its formation, passing through the "bottleneck" of low numbers ("bottleneck" effect). It is important founder principle. It was discovered by Meyer. Example: There is a large population in a certain area. Several individuals accidentally become isolated (fall on the island). If the conditions in the new place are favorable for life, these animals will form a new population and the genetic characteristics of this population will be largely determined by the genetic properties of those animals that were the founders of this population. The gene pool of the new population will be different from the gene pool of the parent population. Animals-founders are not carriers of all the information that the cat is in the parent population, their gene pool is random and depleted, therefore, does not represent a representative sample of the material of the population. The properties of the new population are determined by chance.

Effects of Genetic Drift

The genetic homogeneity of the population may increase, that is, its homozygosity will increase;

Populations that initially have a similar genetic composition and live in similar conditions may lose this property as a result of gene drift.

Contrary to natural selection, alleles can persist in populations that reduce the fitness of individuals.

Due to population waves (changes in population size), a rapid and dramatic increase in the frequency of rare alleles can occur.

Population waves as an elementary factor of evolution

Population waves - fluctuations in the number of populations. They can be caused by different factors (biotic, abiotic). Both periodic and aperiodic population fluctuations can be observed. The waves of life are an elementary factor in evolution. When population growth is balanced, then its number fluctuates around some more or less constant value. Often fluctuations can be caused by seasonal (annual) changes (humidity, temperature, availability of food).

Classification of population waves

1 type- Periodic fluctuations in population. Org-we are living for a short time. Har-but for insects, 1-year-old plants, most fungi and microorganisms. In animals and plants, seasonal fluctuations are not equally reflected in different age and sex groups in the population.

type 2 are aperiodic fluctuations. They depend on a complex combination of a number of factors: on relationships favorable for a given species in food chains (easing the pressure of predators on prey, increasing food resources for prey). Such fluctuations are reflected in many species alive and growing in these biogeocenoses. Example: cycle of population fluctuation in acridoids. For many years they do not migrate, but with an increase in population density, wings appear and migration begins.

3 type- an increase in the number of populations in those areas where there are no their enemies. Example: an outbreak of rabbits in Australia.

4 type- rare non-periodic population fluctuations associated with natural disasters - the destruction of biogeocenoses or entire landscapes. Example: several dry years can cause changes in the appearance of large areas (the advance of meadow vegetation on swamps, the burning of peat bogs).

All factors that affect the number of populations are divided into:

density-independent (when there is no dependence on the size of the population). This includes abiotic factors (harsh winter, storm, drought). They can lead to a sharp decrease in the number of different organisms, which occurs regardless of their initial density. The factor driving the change is not affected by the change because abiotic.

density-dependent if their effect on the population is a function of density (food supply. intraspecific competition). In some cases, biotic factors depend on density in a straight line. So, the higher the population density, the stronger the effect of the factor (Ex: the higher the density of plants, the more they shade each other). With an increase in the population density of a species, mechanisms of self-regulation come into play (decrease in the birth rate, increase in mortality, etc.). These mechanisms return the population to its original state. All these are internal regulators of the population. They are triggered automatically as soon as the population size exceeds the threshold value. In the future, a decrease in the number will lead to the fact that there are more food supplies, therefore the birth rate increases, the number grows. Thus, a dynamic equilibrium is achieved in the population.

Fluctuations in abundance in populations are more pronounced in relatively simple ecosystems, where few populations are included in the community.

The evolutionary significance of population waves is a supplier of evolutionary material. The role is especially important in small populations. The action of population waves is static and non-directional.

21. Main eg phylogenesis: divergence, convergence, parallelism and phyletic evolution.

1) Divergence- the emergence of differences on the basis of the 1st and the same organization. Expenses and arr-e of two species from one, possess similarity. Сх-in is explained by kinship, and differences are adapted to the conv. environment. The reason is the consumption of various environmentalists. niches and intergroups. show jumping results in competition between two ecologists. groups, in each of which the individuals most different from the other group receive an advantage. Fur-m is based on isolation, heritage. change, population. waves and natural selection.

On microevolution. level, the process is reversible (2 populations can interbreed and exist as one). At the macro level, PR is irreversible. The new view cannot merge with the parent. There are types of divergence: 1) dichotomous branching (two forms are formed), 2) adaptive radiation (many forms). Divergence - main. form of phylogeny.

2) Phyletic Evol.- Gradual evolution. changes within a phylogenetic line that go in the same direction. One species, gradually transforming, can give rise to another. That. it is evolution over a period of time without divergence.

3) Convergence- phenomenon, opposite divergence. The image of similar signs in unrelated groups of org-in. The emergence of similar adaptations occurs (in the same conditions of the environment in different organisms). Shark, dolphin, ichthyosaur body shape.

4) Parallelism- an independent image of similar recognitions in kinship. org groups. The similarity is explained by kinship and adaptations to similar conditions; the differences are associated with the pr-mi divergence of the parent org-in (fur seal, walrus, seal). They come to a similar structure of the body and limbs. 2 types of parallelism:

• Synchronous - which occurs at the same time in different groups of organisms (the evolution of 2 groups of mammals of hoofed animals: extinct representatives of the ot liptaptern from South America and the ancestors of the modern horse 5-toed phenopodus).

• Asynchronous - independent development in a similar direction of phylogenetically close groups at different times (development of saber teeth 4 times in 2 independent branches).

Parallelisms divided into different groups according to physiology, ecologist, biochemical, signs. Parallel evolution is explained by the common gene structure of the parent groups and changes. In close taxa, variability is observed (common and dwarf wheat). If similar signs arise on the basis of similar organs, this will lead to convergence, if on the basis of homologous ones - to parallelism.

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Chromosomes are nucleoprotein structures in the nucleus of a eukaryotic cell (a cell containing a nucleus) that become easily visible at certain phases of the cell cycle (during mitosis or meiosis). Chromosomes are a high degree of condensation of chromatin, constantly present in the cell nucleus. The term was originally proposed to refer to structures found in eukaryotic cells, but in recent decades, bacterial chromosomes have been increasingly spoken of. Chromosomes contain most of the genetic information.

There are such types of chromosomes: equal arms (metacentric), (centromere in the middle, and arms of equal length); unequal arms (submetacentric), the centromere is displaced, not in the middle of the chromosome, the length of the arms is unequal; rod-shaped (acrocentric), the centromere is shifted to one of the ends of the chromosome, one of the arms is very short.

The chromosome, as a complex of genes, is an evolutionarily established structure that is characteristic of all individuals of a given species. The location of genes on a chromosome plays an important role in their functioning.

A change in the number of chromosomes in the karyotype (chromosome set) of a person usually leads to various diseases. The most well-known and common chromosomal disease in humans is Down syndrome, which is caused by trisomy (an extra chromosome) on the 21st chromosome. Suffer from this disease 0.1-0.2% of humanity. Often due to trisomy of 21 pairs of chromosomes, the fetus dies, but sometimes people suffering from Down syndrome live to old age, although in general they live less. There are also known trisomy on the 13th and 18th pairs of chromosomes - Patau and Edwards syndromes, respectively. People with such chromosome defects die in the first months of life.

Also quite often a person has a change in the number of sex chromosomes. Monosomy X is common among them (out of a pair of chromosomes, a person has only one (X0)) - this disease is called Shereshevsky-Turner syndrome. Less common are trisomy X and Klinefelter's syndrome (XXY, XXXY, XYU, etc.). The factors that determine the male type of development are in the Y-chromosome, the female - in the X. Unlike mutations in somatic chromosomes, mental malformations in patients are less characteristic, within the normal range, and sometimes even higher. However, they often have violations of the development of the genital organs, hormonal imbalance. Malformations of other systems are much less common.

Chromosomes are an intensely colored body, consisting of a DNA molecule associated with histone proteins. Chromosomes are formed from chromatin at the beginning of cell division (in the prophase of mitosis), but they are best studied in the metaphase of mitosis. When the chromosomes are located in the plane of the equator and are clearly visible in a light microscope, the DNA in them reaches maximum helicity.

Chromosomes consist of 2 sister chromatids (doubled DNA molecules) connected to each other in the region of the primary constriction - the centromere. The centromere divides the chromosome into 2 arms. Depending on the location of the centromere, chromosomes are divided into:

the metacentric centromere is located in the middle of the chromosome and its arms are equal;

submetacentric centromere is displaced from the middle of the chromosomes and one arm is shorter than the other;

acrocentric - the centromere is located close to the end of the chromosome and one arm is much shorter than the other.

In some chromosomes, there are secondary constrictions that separate a region called the satellite from the chromosome arm, from which the nucleolus is formed in the interphase nucleus.

Chromosome Rules

1. The constancy of the number. The somatic cells of the body of each species have a strictly defined number of chromosomes (in humans -46, in a cat - 38, in a fruit fly - 8, in a dog -78, in a chicken -78).

2. Pairing. Each chromosome in somatic cells with a diploid set has the same homologous (same) chromosome, identical in size, shape, but unequal in origin: one from the father, the other from the mother.

3. Individuality. Each pair of chromosomes differs from the other pair in size, shape, alternation of light and dark stripes.

4. Continuity. Before cell division, the DNA is doubled and the result is 2 sister chromatids. After division, one chromatid enters the daughter cells and, thus, the chromosomes are continuous - a chromosome is formed from the chromosome.

All chromosomes are divided into autosomes and sex chromosomes. Autosomes - all chromosomes in cells, with the exception of sex chromosomes, there are 22 pairs of them. Sexual - this is the 23rd pair of chromosomes, which determines the formation of the male and female body.

In somatic cells there is a double (diploid) set of chromosomes, in sex cells - haploid (single).

A certain set of chromosomes of a cell, characterized by the constancy of their number, size and shape, is called karyotype.

In order to understand a complex set of chromosomes, they are arranged in pairs as their size decreases, taking into account the position of the centromere and the presence of secondary constrictions. Such a systematized karyotype is called an idiogram.

For the first time, such a systematization of chromosomes was proposed at the Congress of Geneticists in Denver (USA, 1960)

In 1971, in Paris, chromosomes were classified according to color and alternation of dark and light bands of hetero- and euchromatin.

To study the karyotype, geneticists use the method of cytogenetic analysis, in which a number of hereditary diseases associated with a violation of the number and shape of chromosomes can be diagnosed.

1.2. The life cycle of a cell.

The life of a cell from its inception as a result of division to its own division or death is called the cell life cycle. Throughout life, cells grow, differentiate, and perform specific functions.

The life of a cell between divisions is called interphase. Interphase consists of 3 periods: presynthetic, synthetic and postsynthetic.

The presynthetic period immediately follows the division. At this time, the cell grows intensively, increasing the number of mitochondria and ribosomes.

During the synthetic period, replication (doubling) of the amount of DNA occurs, as well as the synthesis of RNA and proteins.

During the post-synthetic period, the cell stores energy, achromatin spindle proteins are synthesized, and preparations for mitosis are in progress.

There are different types of cell division: amitosis, mitosis, meiosis.

Amitosis is a direct division of prokaryotic cells and some cells in humans.

Mitosis is an indirect cell division during which chromosomes are formed from chromatin. Somatic cells of eukaryotic organisms divide by mitosis, as a result of which the daughter cells receive exactly the same set of chromosomes as the daughter cell had.

Mitosis

Mitosis consists of 4 phases:

Prophase is the initial phase of mitosis. At this time, DNA spiralization and shortening of chromosomes begin, which from thin invisible chromatin threads become short thick ones, visible in a light microscope, and arranged in the form of a ball. The nucleolus and the nuclear envelope disappear, and the nucleus disintegrates, the centrioles of the cell center diverge along the poles of the cell, and the fission spindle threads stretch between them.

Metaphase - chromosomes move towards the center, spindle threads are attached to them. Chromosomes are located in the plane of the equator. They are clearly visible under a microscope and each chromosome consists of 2 chromatids. In this phase, the number of chromosomes in a cell can be counted.

Anaphase - sister chromatids (appeared in the synthetic period when DNA is duplicated) diverge towards the poles.

Telophase (telos Greek - end) is the opposite of prophase: chromosomes from short thick visible ones become thin long ones invisible in a light microscope, the nuclear envelope and nucleolus are formed. Telophase ends with the division of the cytoplasm with the formation of two daughter cells.

The biological significance of mitosis is as follows:

daughter cells receive exactly the same set of chromosomes that the mother cell had, so a constant number of chromosomes is maintained in all cells of the body (somatic).

all cells divide except sex cells:

the body grows in the embryonic and postembryonic periods;

all functionally obsolete cells of the body (epithelial cells of the skin, blood cells, cells of the mucous membranes, etc.) are replaced by new ones;

processes of regeneration (recovery) of lost tissues occur.

Diagram of mitosis

When exposed to unfavorable conditions on a dividing cell, the spindle of division can unevenly stretch the chromosomes to the poles, and then new cells are formed with a different set of chromosomes, a pathology of somatic cells (autosomal heteroploidy) occurs, which leads to diseases of tissues, organs, body.

Chromosomes are the nucleoprotein structures of a eukaryotic cell, which store most of the hereditary information. Due to their ability to self-reproduce, it is the chromosomes that provide the genetic link between generations. Chromosomes are formed from a long DNA molecule, which contains a linear group of many genes, and all the genetic information, whether it be about a person, animal, plant, or any other living being.

The morphology of chromosomes is related to the level of their spiralization. So, if during the interphase stage the chromosomes are maximally deployed, then with the onset of division, the chromosomes actively spiralize and shorten. They reach their maximum shortening and spiralization during the metaphase stage, when new structures are formed. This phase is most convenient for studying the properties of chromosomes and their morphological characteristics.

The history of the discovery of chromosomes

Back in the middle of the nineteenth century before last, many biologists, studying the structure of plant and animal cells, drew attention to thin filaments and the smallest ring-shaped structures in the nucleus of some cells. And now the German scientist Walter Fleming, using aniline dyes to process the nuclear structures of the cell, what is called "officially" opens the chromosomes. More precisely, the discovered substance was called “chromatid” by him for its ability to stain, and the term “chromosomes” was introduced into use a little later (in 1888) by another German scientist, Heinrich Wilder. The word "chromosome" comes from the Greek words "chroma" - color and "somo" - body.

Chromosomal theory of heredity

Of course, the history of the study of chromosomes did not end with their discovery, so in 1901-1902, American scientists Wilson and Saton, independently of each other, drew attention to the similarity in the behavior of chromosomes and Mendeleian factors of heredity - genes. As a result, scientists came to the conclusion that genes are located on chromosomes and it is through them that genetic information is transmitted from generation to generation, from parents to children.

In 1915-1920, the participation of chromosomes in the transmission of genes was proved in practice in a whole series of experiments made by the American scientist Morgan and his laboratory staff. They managed to localize several hundred hereditary genes in the chromosomes of the Drosophila fly and create genetic maps of the chromosomes. Based on these data, a chromosome theory heredity.

The structure of chromosomes

The structure of chromosomes varies depending on the species, so the metaphase chromosome (formed in the metaphase stage during cell division) consists of two longitudinal threads - chromatids, which are connected at a point called the centromere. The centromere is the part of the chromosome that is responsible for the separation of sister chromatids into daughter cells. She also divides the chromosome into two parts, called the short and long arms, she is also responsible for the division of the chromosome, since it contains a special substance - the kinetochore, to which the division spindle structures are attached.

Here the picture shows a visual structure of the chromosome: 1. chromatids, 2. centromere, 3. short arm of chromatids, 4. long arm of chromatids. At the ends of chromatids are telomeres, special elements that protect the chromosome from damage and prevent fragments from sticking together.

Shapes and types of chromosomes

The sizes of chromosomes of plants and animals vary considerably: from fractions of a micron to tens of microns. The average lengths of human metaphase chromosomes range from 1.5 to 10 microns. Depending on the type of chromosome, its ability to stain also differs. Depending on the location of the centromere, the following forms of chromosomes are distinguished:

• Metacentric chromosomes, which are characterized by a median location of the centromere.
• Submetacentric, they are characterized by an uneven arrangement of chromatids, when one shoulder is longer and the second is shorter.
• Acrocentric or rod-shaped. Their centromere is located almost at the very end of the chromosome.

Functions of chromosomes

The main functions of chromosomes, both for animals and for plants and in general for all living beings, are the transfer of hereditary, genetic information from parents to children.

Set of chromosomes

The value of chromosomes is so great that their number in cells, as well as the characteristics of each chromosome, determine the characteristic feature of a particular biological species. So, for example, the fruit fly has 8 chromosomes, the y - 48, and the human chromosome set is 46 chromosomes.

In nature, there are two main types of chromosome sets: single or haploid (contained in germ cells) and double or diploid. The diploid set of chromosomes has a paired structure, that is, the entire set of chromosomes consists of chromosome pairs.

Human chromosome set

As we wrote above, the cells human body contain 46 chromosomes, which are combined into 23 pairs. Together they make up the human chromosome set. The first 22 pairs of human chromosomes (they are called autosomes) are common for both men and women, and only 23 pairs - sex chromosomes - differ in different sexes, it also determines the gender of a person. The totality of all pairs of chromosomes is also called a karyotype.

This species has a human chromosome set, 22 pairs of double diploid chromosomes contain all our hereditary information, and the last pair is different, in men it consists of a pair of conditional X and Y sex chromosomes, while in women there are two X chromosomes.

All animals have a similar structure of the chromosome set, only the number of non-sex chromosomes in each of them is different.

Genetic diseases associated with chromosomes

Violation of the chromosomes, or even their very wrong number is the cause of many genetic diseases. For example, Down syndrome appears due to the presence of an extra chromosome in the human chromosome set. And such genetic diseases as color blindness, hemophilia are caused by malfunctions of existing chromosomes.

Chromosomes, video

And in conclusion, an interesting educational video about chromosomes.

This article is available at English language — .

Sometimes they give us amazing surprises. For example, do you know what chromosomes are and how they affect?

We propose to understand this issue in order to dot the i's once and for all.

When looking at family photos, you might have noticed that members of the same kinship are similar to each other: children look like parents, parents look like grandparents. This similarity is passed down from generation to generation through amazing mechanisms.

All living organisms, from single-celled to African elephants, have chromosomes in the cell nucleus - thin long threads that can only be seen with an electron microscope.

Chromosomes (ancient Greek χρῶμα - color and σῶμα - body) are nucleoprotein structures in the cell nucleus, in which most of the hereditary information (genes) is concentrated. They are designed to store this information, its implementation and transmission.

How many chromosomes does a person have

As early as the end of the 19th century, scientists found that the number of chromosomes in different species is not the same.

For example, peas have 14 chromosomes, y - 42, and in humans - 46 (i.e. 23 pairs). Hence, it is tempting to conclude that the more there are, the more complex the creature that possesses them. However, in reality this is not at all the case.

Of the 23 pairs of human chromosomes, 22 pairs are autosomes and one pair are gonosomes (sex chromosomes). Sexual have morphological and structural (composition of genes) differences.

At female body a pair of gonosomes contains two X chromosomes (XX pair), while the male has one X and one Y chromosome each (XY pair).

It is on what will be the composition of the chromosomes of the twenty-third pair (XX or XY) that the sex of the unborn child depends. This is determined during fertilization and the fusion of the female and male reproductive cells.

This fact may seem strange, but in terms of the number of chromosomes, a person is inferior to many animals. For example, some unfortunate goat has 60 chromosomes, and a snail has 80.

Chromosomes consist of a protein and a DNA (deoxyribonucleic acid) molecule, similar to a double helix. Each cell contains about 2 meters of DNA, and in total there are about 100 billion km of DNA in the cells of our body.

An interesting fact is that in the presence of an extra chromosome or in the absence of at least one of the 46, a person has a mutation and serious developmental abnormalities (Down's disease, etc.).