In 1906, W. Batson and R. Pennet, spending the crossing of the plants of the fragrant peas and analyzing the inheritance of the form of pollen and the color of the flowers, found that these signs do not give an independent distribution in the offspring, hybrids always repeated the signs of parental forms. It became clear that not for all signs is characterized by an independent distribution in the offspring and free combination.

Each body has a huge number of signs, and the number of chromosomes is small. Consequently, each chromosome carries not one gene, but a whole group of genes responsible for the development of various signs. Studying the inheritance of signs whose genes are localized in one chromosome T. Morgan. If Mendel spent his experiments on the pea, the fruit flush of the Drozophile became the main object for Morgan.

Drozofila every two weeks at a temperature of 25 ° C gives numerous offspring. The male and female are clearly distinguishable - the male belt is less and darker. They have only 8 chromosomes in the diploid set, quite easily multiply in test tubes at an inexpensive nutrient medium.

Crossing a flock of drosophila with a gray body and normal wings with a flour with a dark color of the body and the inchareage wings, in the first generation, Morgan received hybrids having a gray body and normal wings (gene, which determines the gray color of the abdomen, dominates the dark color, and the gene caused by The development of normal wings - over the gene is underdeveloped). When analyzing the exercise of the female F 1 with the male, who had recessive signs, was theoretically expected to obtain offspring with combinations of these signs in the ratio of 1: 1: 1: 1. However, in the offspring, individuals were clearly dominated with signs of parental forms (41.5% - gray long, and 41.5% - black with embossed wings), and only a small part of the flies was different than the parents, a combination of signs (8.5% - Black long and 8.5% are gray with staple wings). Such results could only be obtained if the genes responsible for the color of the body and the shape of the wings are in the same chromosome.

1 - increasing gametes; 2 - cross-board grounds.

If the generating genes and wing form genes are localized in the same chromosome, then with this crossing, two groups of individuals, repeating the signs of parental forms, should have been obtained, since the maternal body should form gamets of only two types - AB and AB, and paternal - one type - AB . Consequently, two groups of individuals having the AVA and AABB genotype should be formed in the offspring. However, the offspring appears individuals (albeit in minor quantities) with recompatible features, that is, having a Gotype ABB and AAVB. In order to explain this, it is necessary to recall the mechanism for the formation of genital cells - Meiosis. In the protopase of the first meiotic division, homologous chromosomes are conjugated, and at this moment the exchange of plots can occur between them. As a result of the crosslinker, in some cells, the chromosome sections between the genes A and B occurs, AB and AB gements appear, and, as a result, four groups of phenotypes are formed in the offspring, as with free gene combination. But, since the crosslinker occurs when it is small, the numeric ratio of phenotypes does not correspond to the 1: 1: 1: 1 ratio.

Clutch group - Gennes localized in one chromosome and inherited together. The number of clutch groups corresponds to a chromosome haploid set.

Captured inheritance - Inheritance of signs whose genes are localized in one chromosome. The clutch force between genes depends on the distance between them: the further genes are located apart, the higher the crosslinker frequency and vice versa. Full clutch - A variety of adhesive inheritance, in which the genes of the analyzed features are located as close to each other that the crossingover between them becomes impossible. Incomplete clutch - A variety of adhesive inheritance, in which the genes of the analyzed features are located at some distance from each other, which makes it possible to the crossliner between them.

Independent inheritance - Inheritance of signs whose genes are localized in different pairs of homologous chromosomes.

Unknown gamets - Gameti, in the process of the formation of which the cross hinge did not occur.

Nedekbinnants - Hybrid individuals, who have the same combination of signs, like parents.

Recombinants - Hybrid individuals having a different combination of signs than parents.

The distance between the genes is measured in morganidah - Conditional units corresponding to the percentage of cross-gaming weights or percentage of recombinants. For example, the distance between the genes of the gray color of the body and long wings (also the black color of the body and the inchasal wings) in Drosophila is 17%, or 17 morganes.

DiGaterozigot, dominant genes can be located in one chromosome ( cis-phase), or in different ( trans Phase).

1 - the mechanism of the cis-phase (unknown gemnets); 2 - the trans-phase mechanism (non-surveying grounds).

The result of T. Morgan's research was the creation of them chromosomal theory of hereditary:

1. genes are located in chromosomes; Various chromosomes contain an unequal number of genes; The set of genes of each of the non-homologous chromosomes is unique;
2. each gene has a certain place (locus) in the chromosome; In identical locus, homologous chromosomes are allelic genes;
3. genes are located in chromosomes in a certain linear sequence;
4. genes localized in one chromosome are inherited together by forming a clutch group; The number of clutch groups is equal to the haploid set of chromosomes and constantly for each type of organisms;
5. the adhesion of genes may be disturbed in the crosslinker process, which leads to the formation of recombinant chromosomes; The crosslinker frequency depends on the distance between the genes: the greater the distance, the greater the grade of the crosslinker;
6. each species has a set of chromosomes-karyotype characteristic of it.

Go to lectures number 17. "The basic concepts of genetics. Mendel laws »

Captured inheritance. G. Mendel published the results of his research in 1865, but then his discoveries remained unnoticed. Only in 1900, K-Korrens (Germany), G. de Fris (Holland) and E. Cherk (Austria), independently of each other were found in different plant species the same patterns of inheritance of signs as the city of Mendel. English Genetics W. Baton confirmed Mendel's laws on animals. The requesting of Mendel's laws caused a deep interest in learning the patterns of inheritance of signs and contributed to the rapid development of genetics.

In 1902, a German cytologist and embryologist T. B O V E R and presented evidence of chromosome participation in the transmission processes of hereditary information. He showed, for example, that normal development sea hedgehog Perhaps only with all chromosomes. This connection was noticed in 1903 and the American cytologist. With Etton. So received a substantiation of the assumptions of Mendel

on hereditary factors, the presence of a single set of these factors in gates and double - in the zygotes. In 1909, Danish biologist V. Johansen introduced the concept of S.gen: /.

In 1910, the American geneticist T. Morgan experimentally proved that the genes are located in chromosomes. Numerous surroundings of Morgan and his students led to a number of major discoveries that have formed the basis chromosomal theory of heredity.One of its provisions can be formulated as follows: the genes are located in chromosomes in linear order and occupy certain areas - loci, and the allele genes are in the same docus of homologous chromosomes.

The law of independent inheritance (the third law of Mendel) is fair if the non-allele genes are in different pairs of chromosomes. However, the number of genes in living organisms is much greater than the number of chromosomes. For example, U. man about 25 thousand genes, and the number of chromosomes -

23 pairs (2 n \u003d 46); At fruit fly drosophila Approximately 14 thousand genes and only 4 pairs of chromosomes (2 n \u003d eight). Consequently, each chromosome contains many genes. Will genes localized in one chromosome, inherit independently? Obviously, no.

The genes located in one chromosome form a clutch group and are inherited together.Joint inheritance of genes T. Morgan offered to call coupled inheritance(Unlike independent). Each pair of homologous chromosomes contains genes controlling the same signs, so the number of clutch groups is equal to the number of pairs of chromosomes.For example, a person has 23 clutch groups, and drosophila - 4.

You know that with an independent inheritance, the digerozygous part, for example \u003d ^ \u003d, forms four types of Games in an equal ratio, i.e., 25%: L in, oh, and in and aB. This is due to the fact that non-allele genes are in different pairs of chromosomes. If they are located in homologous chromosomes, it would be expected that the digeterosigot will produce only two types of ha aB

method: 50. % AU and 50. % aB (Please note that the adhesive genes are recorded in one chromosome).

However, T. Morgan discovered that in most cases the digerozygous individuals form not two, but four types of weights. In addition to expected AU and aB Gamets with new combinations of genes are also formed: Ay and aB Only in a smaller percentage ratio. Consider one of the experiments of T. Morgan, in which the inheritance of adhesive genes has been studied drosophila.

If you clean the fruit or vegetables and do not immediately throw off the cleaning or leave the fruit on the table for several days, then you can see how small flies of about 2-3.5 mm in size will be swirling around the residues of food. it drosophila - Fruit flies, the family of insects of the detachment docking (Fig. 95). Usually, drosophiles have red eyes and a yellow-colored abdomen. The life cycle of the Drozophil is short: Development from the egg to the semi-natural individual at 25 ° C takes 10 days. Small sizes, high fertility, simplicity of cultivation and a number of other features for a long time made drosophil to the main object of genetics. Not one Nobel laureate, except for his intelligence, owes her with his scientific achievements.

By crossing the clean line of Drozophil, having a gray body and normal (long) wings, with a clean line, the individuals of which had a black body and embossed wings, the hybrids of the first generation were obtained (Fig. 96). All of them in accordance with the law of uniformity were gray with normally developed wings. Consequently, Drozophil has a gray body (BUT) fully dominates black (a), and normal wings (IN) - Above the stuffy ( b.). All first generation hybrids are digerozyges.

Then the analyzing crossing was performed (Fig. 97). The digerozygous female from the hybrid generation was crossed with a recessive digomozigo male (black body and ridiculous wings). In the offspring, 41.5% of individuals were obtained with a gray body, normal wings and black bodies, with a similar wings, as well as 8.5% flies with a gray body, a similar wings and a black body, normal wings.

If the genes that determine the body color and the development of wings were in different vapor chromosomes, the ratio of phenotypic classes would be equal to 25%. But this was not observed, it means that the genes are in homologous chromosomes and inheritated.

Despite the adhesion of genes, AUthe female produced not two, but four types of weights. However, heams with the initial combinations of adhesive genes was formed much more (AU and aB together amounted to 83%) than with their new combinations (the amount Ay and dv equal to 17%).

It was found that the reason for the appearance of chromosomes with new combinations of parental genes is crossingringer.You remember that this process takes place in the moriza profound I and is the exchange of relevant areas between homologous chromosomes. In this way, the crossover hinders the full (absolute) adhesion of genes.Gamets, which are formed as a result of crosslinker, and individuals that develop with the participation of such heams are called crossover or recombinant. In the experiment considered, Gameta Ay and aU were crossover, and gamets AU and aB - Unknown (see Fig. 97).

Crossingrover between specific adhesive genes occurs with a certain probability (frequency). To calculate the frequency of cross (RF, from English. rECOMBINATION FREQUENCY. - The frequency of recombination) can be used by the following formula:

Thus, between genes BUT and IN, Controlling the color of the body and the length of the wings of drosophila, the crossover occurs with the frequency: rF AB \u003d. 17 %.

Further studies conducted by T. Morgan and its employees showed that the crosslinker frequency is proportional to the distance between the genes located in one chromosome.The larger the distance between the detachable genes, the more often a crosslinker occurs between them. And vice versa, the closer to each other are genes, the smaller the crosslinker's frequency between them. What explains this pattern?

In Profase I, MEIOS, with the conjugation of homologous chromosomes, the formation of crossroads between chromatids is carried out arbitrarily, in any respective areas. Consider Figure 98.

Genes. BUT and IN (or but. and B) are relatively close to each other. The likelihood that the crossing will occur on the plot that shares these genes is small. Genes. BUT and D. (or but. and d) Located at a considerable distance from each other. Therefore, the likelihood that chromatids will cross on any plot between them, much higher. It means that the larger the distance between the genes, the more often they are divided into crossing rider.

Thus, the frequency of the cross hinge allows you to judge the distance between the genes. In honor of T. Morgana, the unit of measurement of the distance between the genes was named blink and yes or that the same, Santi Morgay and Yes (cm).

Morganide (Santimorganide, cm) is a genetic distance on which the crossingler occurs with a probability of 1%.

The biological importance of the crossfield is extremely large. As a result of this process, new combinations of parental genes arise, which increases the genetic diversity of the offspring and expands the possibilities of adapting organisms to various environmental conditions.

Genetic maps. T. Morgan and employees of his laboratory showed that the knowledge of the frequency of the crosslinker between the detachable genes allows you to build genetic maps of chromosomes. The genetic card is a scheme of the mutual arrangement of genes in one clutch group, taking into account the distances between them (Fig. 99).

Chromosome genetic maps have already been compiled for a person, many species of animals, plants, mushrooms and microorganisms. The presence of a genetic map indicates a high degree of study of a particular type of body and is a great scientific interest. Such an organism is an excellent facility for further experimental work that has not only scientific, but also practical importance. In particular, knowledge of genetic cards allows you to plan work on obtaining organisms with certain combinations of features, which is widely used in breeding practice. Genetic maps of human chromosome are used in medicine for the diagnosis and treatment of a number of hereditary diseases.

The main provisions of the chromosomal theory of heredity.

1. Genes in chromosomes are located linearly, in a certain sequence. Allel genes are in the same chromosome homologous locus.

2. The genes located in one chromosome form a clutch group and are inherited together. The number of clutch groups is equal to the number of pairs of chromosomes.

3. The adhesion of genes may be impaired as a result of a crosslinker occurring in the conjugation of homologous chromosomes in Profase I of Maiz.

4. The crosslinker frequency is proportional to the distance between the genes: the greater the distance, the higher the frequency of the crosslinker, and vice versa.

B. For a unit of distance between the detachable genes, 1 morgane was adopted - the distance on which the crossingler occurs with a probability of 1%.

02-Sep 2014 | No comments | Lolita Ocolnova

Captured inheritance

After the discovery began to notice that these laws were not always triggered.

For example: crossed the digerozygous female of drosophila with gray body and normal wings With the male S. black body and shortened wings .

Gray body and normal wings - dominant signs.

According to the laws of Mendel, crossing scheme is this:

But the practical result of crossing is different.

As a rule, a splitting of 1: 1 is observed in the offspring,

phenotypes of offspring: Gray Body, Normal Wings and black Body, Cropped Wings.

Does not work . Why so? Does the laws of Mendel really do not work? Of course, no, the laws of nature can be "violated", only if it allows another law (exception to the rule).

Let's figure it out ...

• information about each sign carries a certain gene;
• genes are in chromosomes.

Naturally, the number of chromosomes is significantly less than the number of genes, therefore several genes are encoded in one chromosome.

Genes in the same chromosome are inherited together, that is captured .

And the genes in different chromosomes are inherited independently

since during the gamenisse of chromosomes is randomly distributed, therefore, two non-delicate the gene can get together in one gamet, and may not.

The genes in the same chromosome will necessarily be in one gamete.

In the example we considered earlier, we can notice:gray body It is inherited to S.normal wingsand black body It is inherited to S.shortened wings.

The body color genes and the length of the wings are in the same chromosome.

Female DiGaterozigot, there are two homologous chromosomes:

in one of the homologous chromosomes, genes are encoded gray Body and Normal Wings,

in another - genes

But only two types of Games are obtained - signs of body color and sized wing "indivisible"

Father's individual According to these features, Digomozygous:

in one homologous chromosome genes black body and shortened wings,

and in another homologous chromosome as well.

All signs encoded in one chromosome form the so-calledclutch group .

Signs from one clutch group are inherited together.

And how can you guess

quantity clutch groups Equally, the number of chromosomes in the haploid set.

Examples of tasks

Task 1:

A little different design: captured signs are recorded on "chopsticks", for example, female genotypes from our task should be recorded like this:

• sticks mean homologous chromosomes in which genes are localized
• the letters on one side of the sticks denote the genes linked with each other.

That is, the record says:

signs of AV clips each other; AB signs are also linked to each other.

• the position of genes in genotype 1) called Cis-Regulations: AB \\\\ AB (dominant signs on one chromosome, recessive on another)
• position 2) called trans-Regulations:AB \\\\ AB.

We will examine on the example:

1) In the condition of the task, all the signs are immediately indicated, fill in the table:

2) The first plant is digerozygically, it is said that dominant signs are localized in one chromosome, that is, adhesive. Moreover, dominant signs are located on one homologous chromosome, therefore, on another homologous chromosome, recessive features are located (cis-position). The genotype of the first plant: AB \\\\ AB.

We receive only two types of weights (since signs of clips):

AB I.aB.

3) Since the second plantshowedisrecessive Signs, we conclude that it is digomozigo. And its genotype: AB \\\\ AB.Only one grade Games is formed:aB.

4) Finally, make a crossing scheme:

And answer the last question of the task - about the law:

the law of adhesive inheritance is manifested, it says:genes localized in one chromosome form a clutch group and inherit together .

But it happens that even genes from one clutch group (localized in one chromosome) Inherited separately, that is, "discharge".

For example, take crossing from the previous task.

With the same crossing, 4 phenotypic groups (instead of laid 2) can be obtained in the offspring, as with independent inheritance. This is explained by the opportunity crossinchiera between homologous chromosomes (those who do not understand what it is about, I advise you to read the articlecross Hopeer ).

Suppose if the individual is a signAB Captured, then in the formation of Games if a crosslinker will occur, there is a possibility that the chromosome section in which one of the "thrust" genes is encoded to another homologous chromosome, and the clutch will break. On the example of our task, in the case of a crosslinker, crossing will be as follows:

A digerozygous plant forms two more grades, due to crossing leaders. Gamets, in the formation of which, a crosslinker occurred (in this task itAB and aB) Called crossover . Statistically, the percentage of crossover games fewer increasing.

And, accordingly, the closer to each other are the genes in the chromosome, the probability of their separation.

This dependence of the probability of separation of crossing hen genes and the distance between genes was so "convenient" that the distance between genes is measured as a percentage of the probability of their separation during crosslinic drive. According to the formula:

Where:

• x is the probability of separation of genes in percent
• a is the number of individuals formed from cross-game Games, n - the number of all individuals.
• And 1% of the probability of gene separation took per unit distance between these genes.

This unit is called Morganida. Called a unit in honor of the famous genetics that studied this phenomenon

1 Morganida \u003d 1% probability that the linked genes, as a result of crosslinker, will be on different homologous chromosomes

Task 2:

1) make a table of signs

2) Once in the condition it is said that they conducted an analyzing crossing, which means the second plant digomozigo on recessive features, its genotype: AB \\\\ AB.

3) 4 phenotypic groups received in the offspring. Since the sprnotals are clicked, it obviously had a cross hinge. Also, the appearance of four phenotypic groups in the analyzing crossing indicates the digerozygousness of the first plant. It means its genotype: either AB \\\\ AB, or AB \\\\ AB.

To determine in which position of genes - cis or trance, you need to look at the ratio in the offspring. Pthe crossover gaming root is less than unknown, therefore individuals who have come from unconsuming games are more.

These individuals: 208 high plants with smooth endosperm, 195 - low with rough endosperm

They have a dominant sign inherited with dominant, and recessive with recessive. Consequently, the genes in the parent digerozygous individual in the CIS position: AB \\\\ AB.

4) Crossing scheme:

Crossing gamets and individuals obtained from them are red. These individuals are smaller, since smacks are formed less. If the parent digerozygous individuals would be in the trans position, in the offspring, on the contrary, there would be more individuals with signs: high rough, and low smooth.

5) Determine the distance between the genes.

To do this, we calculate the likelihood that the signs will be divided as a result of a crosslinker.

According to the formula:

x \u003d 9 + 6208+ 195+ 9 + 6 × 100% \u003d 15418 × 100% \u003d 3.59%

That is, the distance between the genes \u003d 3.59 Morganide.

The law of independent distribution of signs (the third state of Mendel) is violated if the genes that determine different signs are in the same chromosome. Such genes are usually inherited together, i.e. it is observed captured inheritance. The phenomenon of the adhesive inheritance was studied by Thomas Morgan and his employees and therefore wears the name morgana Law.

T. Morgana law can be formulated as follows: genes in one chromosome form a clutch group and are often inherited together, while the frequency of the joint inheritance depends on the distance between the genes (the closer, the more often).

The reason why the adhesive inheritance is violated is a crosslinker flowing in meyosis with chromosomes conjugation. At the same time, homologous chromosomes exchange their sections, and thus the previously adhesive genes may be in different homologous chromosomes, which causes an independent distribution of signs.

For example, a gene A Coupled with a genome B (AB), the homologous chromosome are recessive alleles of the respective genes (AB). If the homologous chromosomes are almost never exchanged homologous chromosomes in the area so that one gene goes to another chromosome, and the other remains in the same, then such an organism forms a gamet only in two types: AB (50%) and AB (50%). If the exchange of relevant areas occurs, some percentage of Games will contain AB and AB genes. Usually their percentage is less than with an independent distribution of genes (when A and B are in different chromosomes). If, with an independent distribution of all types of Games (AB, AB, AB, AB), it will be 25%, then in the case of a linked inheritance, Games AB and AB will be less. Than they are less, the closer the genes are located to each other in the chromosome.

The inheritance seized with the floor is highlighted when the gene under study is in the gender (usually x) chromosome. In this case, the inheritance of one trait is being studied, and the second is the floor. If the inherited feature is adhesive with the floor, it is in different ways in the reciprocal crossing (when the female parent has a sign, then male).

If the mother has a genotype AA, and the father has a dominant sign (exactly there is one gene A), then in the case of a clutch with the floor, all the daughters will have a dominant sign (in any case, it will receive its only X-chromosome from his father, and all sons - recessive (Father gets y-chromosome, in which there is no appropriate gene, and from the mother - in any case, gene a). If the sign was not adhesive with the floor, then among both sexes of children could have dominant signs.

When the genes studied are clicked in an autosome, such a clutch is called autosomal. The clutch is called complete if parental combinations of alleles are not violated from generation to generation. It happens very rarely. It is usually observed incomplete adhesive inheritance that violates both the third law of Mendel and the Morgana law (in its abbreviated wording: genes in one chromosome are inherited together).

Genes in chromosome are located linearly. The distance between them is measured in centimorgana (cm). 1 cm corresponds to the presence of 1% of crossover games. Conducting various crossings and statistically analyzing the descendants, scientists identify the clutch genes, as well as the distance between them. Based on the data obtained, genetic maps are being built, which reflects the localization of genes in chromosomes.

The biological basis of the third law of Mendel is the independent discrepancy of chromosomes during meyosis. Therefore, the third law is faithful only for genes located in different chromosomes.

If the genes are in one chromosome, then they cannot dispense from each other, so they are inherited together (adhesion) is the clutch law (Morgana law). All genes that are in the same chromosome form a clutch group.

With full clutch (it is found, for example, in males drosophyl) a digeterosigot forms only two types of Games.

It is much more commonly occurred by an incomplete clutch when, due to crosslinker, during meyosis, the chromosomes are met. Then the diagelosigot forms 4 types of heams in an unequal ratio: the most part is the ground with a group of clutch, smaller - recombinant gates.

The proportion of recombinant weights depends on the distance between the genes in the chromosome, is measured in conventional units of morganes. The phrase "The distance between genes A and B is equal to 10 Morganid" means that recombinant weights will turn out in the amount of 10% (5% + 5%), and normal - 90% (45% and 45%).

Tests

1. When crossing flies, drosophyl with gray body and normal wings and drosophyl with a dark body and the inferior wings manifests the law of adhesive inheritance, therefore, these genes are located in
A) different chromosomes and curved
B) one chromosome and clips
C) one chromosome and not clips
D) different chromosomes and not clips

2. If the genes are located in different pairs of non-homologous chromosomes, then the law is manifested
A) incomplete domination
B) full domination
C) independent inheritance
D) splitting signs

3. If the genes responsible for coloring and the shape of pea seeds are located in different chromosomes, then in the second generation a law is manifested
A) independent inheritance
B) adhesive inheritance
C) the splitting of signs
D) dominance

4. The number of groups of adhesion of genes in organisms depends on the number
A) pairs of homologous chromosomes
B) allelic genes
C) dominant genes
D) DNA molecules in the core core

5. If the genes responsible for the development of several signs are located in one chromosome, then the law is manifested
A) splitting
B) adhesive inheritance
C) incomplete domination
D) independent inheritance

6. "The genes located in one chromosome are inherited together" is the wording of the law
A) the interaction of genes
B) adhesive inheritance
C) independent inheritance
D) homologous series of variability

7. Which law is manifested when crossing the digerozygous organisms, in which genes, for example, and B, are located in non-homologous chromosomes?
A) full domination
B) incomplete domination
C) independent inheritance
D) adhesive inheritance

8. always inherited genes
A) recessive
B) allelic
C) dominant
D) closely clutch

9. When crossing the drosophyl with gray body and normal wings and drosophyl with the dark body and the inferior wings manifests the law of adhesive inheritance, since the genes responsible for these signs are located in
A) DNA mitochondria
B) different pairs of chromosomes
C) one pair chromosome
D) genital chromosomes

10. What law will appear when crossing if the genes are located in one chromosome?
A) splitting signs
B) adhesive inheritance
C) independent inheritance
D) homologous series

11. According to the Morgan Law, the genes are inherited primarily together if they are located in
A) autosome
B) genital chromosomes
C) one chromosome
D) different homologous chromosomes