Human genome interaction of genes. Interaction of nonallelic genes. Interaction between allelic genes

Lecture 5. Types of interaction between allelic and non-allelic genes

Allelic genes are when each gene determines one trait.

The interaction of allelic genes includes: incomplete dominance, intermediate inheritance, codominance and overdominance.

With incomplete dominance, individual contrasting traits controlled by one pair of allelic genes occupy an intermediate position in homozygous parents in the first generation; all heterozygous individuals are of the same type. In the second generation, when individuals of the first generation are crossed with each other, a 1:2:1 split occurs in both genotype and phenotype. For example, crossing cows with white spots on the body, white belly and legs with bulls with solid coloring produces offspring with solid coloring, but with small spots on the legs or other parts of the body.

With an intermediate nature of inheritance, the offspring in the first generation retain uniformity, but they are not completely similar to any of the parents, as was the case with complete dominance, but have a sign of an intermediate nature. For example, it is known that among sheep, along with normal-eared sheep with an ear length of about 10 cm, the first generation produces offspring exclusively with short ears - about 5 cm in length.

Codominance is when a hybrid individual has equally Both parental characteristics appear. By type of codominance, most antigenic factors of quite numerous blood systems are inherited in different types domestic animals and humans. Also inherited different types proteins and enzymes: hemoglobin, transferrin, amylase, ceruloplasmin.

With overdominance, heterosis appears in first-generation hybrids. Heterosis is the phenomenon of superiority of offspring over parental forms in vitality, growth energy, fertility and productivity. Overdominance is the interaction between genes that are allelic, as a result of which heterozygous individuals are phenotypically superior to both homozygotes. As an example, three different genotypes can be used, such as A1A1, A1A2 and A2A2. By interaction is meant the phenomenon when, with the simultaneous presence of A1 and A2 (in the A1A2 genotype). they synthesize a product or produce a result that is not present when these genes occur separately, as in genotypes A1A1 and A2A2. To illustrate this type of interaction (action between alleles), one blood type in rabbits can be used. Animals of the A1A1 genotype produce antigen 1 (the first antigen), and the A2A2 genotype has antigen 2. Rabbits of the A1A2 genotype synthesize not only antigen 1 and 2, but also the third antigen (antigen 3). Thus, the A1 and A2 genes jointly produce an antigen that they do not produce separately.

With overdominance, heterozygotes turn out to be more viable, but when mating with each other, they split and produce only about 50% heterozygotes.

Genes that influence the development of a trait, localized in different pairs of homologous chromosomes, are called non-allelic. There are several types of interaction of non-allelic genes (neoplasm, complementary, epistasis, modification, polymer).

Sometimes two or more pairs of non-allelic genes influence the same trait. The formation of a trait in this case depends on the nature of their interaction during the development process.

A neoplasm is a type of interaction of genes when, when they are combined in one organism, a completely new form of a trait develops. It is known that in chickens the genes for the rose-shaped and pod-shaped comb are not allelic and the pod-shaped and rose-shaped comb is dominant over the leaf-shaped one. When crossing Wyandotte chickens with a rose-shaped comb (PPcc) with Brahma roosters with a pod-shaped comb (PPCC), the descendants of the first generation (PPCc) as a result of the interaction of two dominant genes P and C develop a new comb shape - nut-shaped. Crossing the descendants of the first generation with each other leads to the production of four different phenotypes in the second generation in the ratio: 9 with genes P and C with a nut-shaped comb, 3 Pcc - with a rose-shaped comb, 3 ppC - with a pod-shaped comb and 1 ppcc - with a leaf-shaped comb. comb Phenotype splitting is 9:3:3:1. In this case, the interaction of the non-allelic genes P and C determines the formation of a new ridge shape, while each of these genes separately exhibits its own effect. An individual with a leaf-shaped comb is a double recessive.

Complementary (complementary) interaction of genes. In the case when a trait is formed in the presence of two dominant non-allelic genes, each of which does not have an independent phenotypic expression, the genes are designated as complementary. For example, when crossing white Minor chickens with white silky chickens, the first generation is colored. For the development of color, it is necessary that the body synthesizes a substance (protein) that causes color and an enzyme that converts this substance into pigment. Usually the ability to synthesize a substance dominates the inability to form it. White Minor cats have the CCoo genotype. They are able to synthesize the substance necessary for the formation of pigment, but are unable to synthesize the enzyme that converts this substance into pigment. White silky chickens have the CCOO genotype. They are unable to synthesize the substance necessary for the pigment, but have the ability to synthesize the enzyme. When such chickens mate with each other (CCoo x CCOO), the descendants of the first generation are colored (CCOO). In this case, pigment was formed as a result of the inclusion in the genotype of birds of the first generation of both dominant genes - C (determining the synthesis of the substance) and O (determining the synthesis of the enzyme). In the second generation of colored birds, 9 parts are expected (S..O..), and white birds - 7 parts (C..oo - 3, ssO.. - 3 and ssoo - 1).

The complementary interaction of genes is apparently responsible for a special type of paralysis of the hind limbs in crossbred dogs obtained from crossing a Great Dane with a St. Bernard. Genetic analysis carried out by Stockard showed that with purebred breeding, paralysis is not observed in both Great Danes and St. Bernards. At the same time, out of 57 first-generation crossbreeds obtained from reciprocal crossings of these breeds and surviving to 3 months of age, only 3 or 4 did not have such a defect. Among the second generation crossbreeds, out of 66 puppies that lived up to 3 months, almost a third were paralyzed. The disease appears suddenly at about 3 months of age. The severity of the disease can vary: from mild paralysis to complete loss of the ability to move independently. A similar disease occurs in some crossbred sniffer dogs.

Epistasis. In this type of interaction, one dominant gene, for example gene C, suppresses the action of another non-allelic dominant gene B. With the SSBB genotype, traits caused by the C gene appear. The gene that suppresses the development of another trait is called epistatic, and the suppressed gene is called hypostatic. For example, in a horse, the gray dominant color, associated with early graying, overshadows all other colors. When crossing a gray horse of the CCBB genotype with a red horse of the CCBB genotype, all descendants of the first generation will be gray with the CCBB genotype. When the descendants of the first generation are crossed with each other in the second generation, a split in phenotype is observed: 12 gray, 3 black and 1 red. The gray allele (C) overrides the effect of other independent color genes. All horses with the C allele in their genotype will be gray. If the C allele is absent, if the B allele is present in the genotype, the horse will be black (ssBB, ssBv) and a horse with the ssBB genotype, a double recessive, will be red in color.

Polymerism. With polymerization, or polymeric (polygenic) inheritance, the same trait is influenced by several different but similarly acting non-allelic genes. Each of these genes enhances the development of a trait. Such uniquely acting genes are called additive. This type of interaction was first established by Nilsson-Ehle while studying the inheritance of the color of oat scales and wheat grains. Polymer genes are designated by one letter with numerical indices: A1, A2, A3, A4, etc.

When crossing individuals that differ in quantitative characteristics, in the first generation there is no complete dominance of the trait of one of the parents, and in the second generation there is no clear splitting, but there are shades of it. The phenotypic ratio is 15:1.

For example, when crossing hens homozygous for two pairs of different recessive alleles (a1a1a2a2), causing unfeathered legs, with roosters homozygous for dominant alleles (A1A1A2A2), all chickens in the first generation have feathered legs. In the second generation, phenotypic classes can only be roughly outlined. All offspring represent a continuous series, from feathered in varying degrees to unfeathered. The ratio of feathered to unfeathered is 15:1.

In chickens, the concept of “brown color” combines a wide range of shades of this color, from very light to dark red-brown. The breeds of this group are widespread and have great industrial importance. Their genetic feature is that the plumage color is determined by the predominance of pheomelanin, which is why these breeds are called the pheomelanin group. There is no specific gene for brown or other plumage coloration in chickens of this group. The variety of shades and intensity of brown tones is controlled by a large number of genes (A1A1A2A2 A3A3A4A4), many of which have an additive effect. The inheritance of pheomelanin colors in the plumage of chickens is subject to the general laws of inheritance of traits.

In sheep, polymer genes and their recessive alleles are known, causing various color modifications (from white to brown or black).

Modifier genes. Genes that do not exhibit their own effects, but enhance or weaken the effect of other genes, are called modifier genes. The study of coloration in mammals has shown that, along with extreme forms with full development of pigment or its absence, a number of genotypically determined transitional forms are observed. There are at least three pairs of modifier genes that affect the amount of red pigment in cattle hair. As a result, in animals homozygous for the recessive red gene, the color intensity ranges from cherry, like in cattle of the red Gorbatov breed, to fawn and almost white with a yellowish tint in cows of the Simmental breed. Modifier genes play a certain role in the formation of resistance to infectious and non-communicable diseases. Hereford cattle have a white head, and when kept on pasture in conditions of strong solar insolation, animals with non-pigmented and weakly pigmented eyelids suffer from eye cancer. With pigmentation of the eyelids, the frequency of the disease decreases, and with intense pigmentation under the same conditions, the disease does not occur. It turned out that the intensity of pigmentation of the skin around the eyes in white-headed animals is hereditary. This indicates the existence of modifier genes of the main gene that determines the white coloration of the head. Thus, through selection, eye cancer can be eliminated.

In chickens, genes known to weaken plumage color are Bl, Sd, pk, ig, mi, Li, lav. In a number of chicken breeds (black Spanish, Orpington, Polish, etc.), under the influence of genes that weaken black pigmentation, the standard color of the plumage is weakened and disrupted. The Li gene, a sex-linked attenuator of brown plumage, turns all areas of brown plumage into pale yellow. The recessive autosomal mutant lavender gene lav turns black feathers into gray and red into fawn.

In rabbits, the modifier gene H is known, which enhances the blue color in the Vienna Blue breed.

In cattle, modifier genes control variegated coloration in the black-and-white group of breeds.

In Karakul sheep, the dominant gene O is a color weakener - black (Arabi) and brown (Kambar).

Task No. 1

Topic 22. Interaction of allelic and non-allelic genes

Self-control issues

1.When do the laws of genetics formulated by G. Mendel apply?

2. In what case does the law of adhesion apply?

3.Who formulated the law of adhesion?

4.Is the linkage between genes absolute?

5.Name the main provisions of the chromosome theory

6.What is the significance of the chromosome theory

1. Read the educational material below.

2.Analyze tables from the application

3.Answer self-control questions.

Genotype is a system of interacting genes. Both allelic and non-allelic genes located in different loci of the same and different chromosomes interact with each other.

Allelic genes enter into relationships such as dominance - recessivity; distinguish between complete and incomplete dominance, codominance, overdominance, and multiple alleles.

Complete Domination– the dominant allele completely hides the presence of the recessive one.

Incomplete dominance there is a manifestation of an intermediate characteristic.

Codominance– manifestation in heterozygotes of characteristics determined by two alleles.

For example, this is how human blood types are inherited (each allele encodes a specific protein, and in heterozygotes both are synthesized.

Overdominance– a dominant gene in a heterozygous state has a stronger manifestation than in a homozygous state. For example, a recessive lethal mutation is known in Drosophila; heterozygotes have greater viability than homozygotes

Multiple alleles; sometimes alleles may include more than two genes. In addition to the main - dominant and recessive - genes, intermediate genes appear, which behave as recessive in relation to the dominant one, and as dominant in relation to the recessive one.

Types of interaction.

1. Cooperation

2.Complementarity

3.Epistasis

4.Polymeria

5.Multiple action (pleotropy)

Cooperation– the appearance of neoplasms due to the combined action of two dominant non-allelic genes, when in a homozygous or heterozygous state a new trait develops that is absent in the parental forms.

Complementarity- a type of inheritance in which non-allelic genes complement each other.

Example :

When crossing yellow budgies with blue individuals, all first-generation hybrids are green. When these green hybrids are crossed with each other, a split is observed in their offspring - 9 parts are green: 3 parts are yellow: parts 3 parts are blue; 1 often white.

Explanation.

The parents were homozygous since all first-generation hybrids are uniform. The appearance of a new variant of the trait (green color) in the first generation cannot be explained by incomplete dominance (since there are white individuals in the second generation).

It can be assumed that in budgerigars the presence of yellow pigment is determined by the dominant allele A, and the presence of blue pigment by the dominant allele B. If the first generation hybrids have dominant alleles A and B, both yellow and blue pigments are synthesized, which together give a green color. In the absence of dominant alleles, some of the second generation hybrids have neither yellow nor blue pigments, and the plumage becomes colorless - white.

P: ♀Aaaaaa x ♂aaaaa

Yellow blue

F 1: ♀AaBv x ♂AaBv

green green

F 2: 9A-B-: 3A – bb: 3aaB-: 1aavv

green yellow blue white

Epitasis- a type of inheritance in which the action of one gene is suppressed by the action of another non-allelic gene.

For example, consider the inheritance of coat color in rabbits.

Dominant gene C – ensures the synthesis of black pigment.

Recessive gene c – does not produce pigment.

There is another pair of alleles (A-a) that affects the distribution of pigment, if already present.

Dominant gene A - causes an uneven distribution of pigment along the length of the hair (the pigment accumulates at its base, while the tip of the hair is devoid of pigment (gray rabbits). The recessive gene (a) does not affect the distribution of pigment.

P: ♀SSAA x ♂SSAA

gray white

F 1 ♀СсАа x ♂ СсАа

Gray gray

Interaction of allelic genes and its types

While studying G. Mendel's laws, we have already become acquainted with the main types of interaction of allelic genes. Based on previously studied material, fill out the table.

Table. Types of interaction between genes of one allelic pair

Interaction of nonallelic genes

Based on the laws of G. Mendel, we can come to the conclusion that there is a fairly strong connection between a gene and a trait, that the genotype is made up of the sum of independently acting genes, and the phenotype is a mechanical combination of individual traits. However, direct and unambiguous connections between a gene and a trait are the exception rather than the rule. The development of a trait in an organism is usually under the control of many genes, and the trait is the result of the interaction of non-allelic genes.

The simplest case of interaction of non-allelic genes is when a trait is controlled by two pairs of alleles. Let's look at some examples of such interaction.

Complementary gene interaction

The phenomenon of gene interaction, in which the presence of two non-allelic genes is necessary for the manifestation of a trait, is called complementarity(from lat. complementum- addition), and the genes necessary for the manifestation of the trait are complementary, or additional.

Let's consider various options for complementary gene interaction.

Alleles of the second gene appear only in the presence of a dominant allele of the geneA. The coloring of mice depends, in the simplest case, on two genes. Mice with genotype ahh lack pigment and have White color. In the presence of a dominant allele A the pigment is produced and the mouse is somehow colored. The specific color is determined by the second gene. Its dominant allele WITH determines grey colour mice, and the recessive allele With- black color. Thus, if we consider homozygous variants, the genotype of gray mice is AASS, black – AAAss, white – aaSS or aass. When crossing a gray mouse AASS with white aass in the first generation everything turns out according to Mendel: all hybrids are gray in color (these are heterozygotes with the genotype AaSs). In F2, as is easy to check, we get 9/16 gray mice, 3/16 black and 4/16 white.

For a trait to manifest itself, dominant alleles of two different genes must be present in the genotype. An example of such complementary gene interaction is the inheritance of fruit shape in pumpkins. In the presence of both dominant alleles, the fruits have a disc-shaped shape, in the presence of one (any!) dominant allele - spherical, and in the absence of dominant alleles - elongated.

For a trait to manifest itself, dominant alleles of two different genes must be present in the genotype, but each dominant allele, in combination with recessive alleles of the other pair, has an independent phenotypic manifestation. For example, in chickens, the pea-shaped crest is determined by one dominant gene, while the rose-shaped crest is determined by another non-allelic, but also dominant gene. When these genes are in the same genotype, a nut-shaped crest develops. If the organism is homozygous for both recessive genes, a simple leaf-shaped comb develops. When crossing dihybrids (all with a nut-shaped comb), in the second generation a splitting occurs in a ratio of 9: 3: 3: 1. But here it is impossible to find independent segregation of each allele in a 3:1 ratio, since in all cases of coincidence in the genotype of both dominant genes, their direct effect is not detected.

Thus, we speak of complementary interaction of non-allelic genes in the case when two non-allelic genes give a new trait, that is, a new formation occurs.

Epistatic gene interaction

The interaction of genes, in which one gene suppresses the action of another, non-allelic to the first, is called epistasis(from Greek epi– above and stasis- stand), and genes that suppress the action of other genes are called suppressor genes, or inhibitor genes(from lat. inhiber– hold), or epistatic genes. The gene being suppressed is called hypostatic.

There are dominant and recessive epistasis.

Dominant epistasis associated with a dominant inhibitor gene. For example, gene I determines the white color of pumpkin fruits; if present, the effect of the gene IN does not appear. With genotype iiBB or iiВb pumpkin fruits have yellow. Finally, if both genes are represented by recessive alleles, the pumpkin fruit is green. The same type can be used to inherit the coat color of dogs, sheep and other animals.

Recessive epistasis is detected when the expression of a gene is suppressed by recessive alleles of another gene. This type of epistasis is illustrated by the inheritance of coat color in house mice. Agouti color (reddish-gray) is determined by the dominant gene A, its recessive allele A gives a black color. Gene from a non-allelic pair IN promotes the manifestation of color, and the gene b is a suppressor and suppresses the effect of the dominant allele A and recessive A. Mice with genotype Аbb indistinguishable in phenotype from individuals with the genotype aabb- all white.

Polymeric gene interaction

Polymerism– a type of interaction of non-allelic genes in which several pairs of non-allelic genes act on the development of one trait. Such genes are called polymer(from Greek policy– a lot and meros- Part). They are denoted by the same letter, but with different indices, which indicate the number of allelic pairs in the genotype that determine the development of a particular trait ( A 1 A 1 A 2 A 2).

There are two variants of polymerization: with the summing effect of genes and without enhancing genes with each other.

The cumulative effect of polymer genes. In this case, the degree of manifestation of the trait depends on the number of dominant alleles in the individual’s genotype. Thus, the red color of wheat grains is determined by two or more pairs of genes. Each of the dominant genes of these alleles determines the red color, while the recessive genes determine the white color of the grains. One dominant allele produces grains that are not very colored. If two dominant alleles are present in the genotype, the color intensity increases. Only when the organism is homozygous for all pairs of recessive genes are the grains not colored. Thus, when crossing dihybrids, a split occurs in the ratio of 15 colored to one white. But out of 15 painted ones, one will have an intense red color, because... contains four dominant alleles, four will be slightly lighter in color, because contain three dominant alleles and one recessive allele in genotypes, six are even lighter with two dominant and two recessive alleles in genotypes, four are even lighter, because have only one dominant and three recessive genes, that is, the true split will be 1: 4: 6: 4: 1.

According to this version of the polymer, skin color, height and weight are inherited in humans. A similar mechanism of inheritance is characteristic of many quantitative, including economically valuable traits: sugar content in beet roots, vitamin content in fruits and vegetables, length of the ear of cereals, length of the ear of corn, animal fertility, milk production of livestock, egg production of chickens, etc.

Polymer genes do not enhance each other. In this case, the splitting in F 2 will be 15:1. Thus, the fruits of the shepherd's purse can be triangular ( dominant trait) and oval (recessive). The trait is controlled by two pairs of polymer genes. If the genotype of a plant has at least one dominant allele from the first or second pair of polymer genes, then the shape of the fruit will be triangular ( A 1 A 2; A 1 a 2; a 1 A 2 ). Only those plants that do not have a single dominant allele in their genotype will have an oval fruit shape - a 1 a 1 a 2 a 2.

Thus, the accumulation of certain alleles in the genotype can lead to changes in the expression of traits.

Multiple gene action

Often a gene affects not one, but a number of traits in an organism. The phenomenon in which one gene can influence the formation of several characteristics of an organism is called pleiotropy(from Greek pleon– more numerous and tropos- turn).

The existence of this phenomenon does not at all contradict the classical concept of “one gene – one protein – one trait”. In a simplified way, the influence of one gene on several traits at once can be represented as follows. As a result of reading information from a gene, a certain protein is formed, which can then participate in various processes, occurring in the body, thus exerting multiple effects. For example, in peas the brown color of the seed coat and the development of pigment in other parts of the plant and the color of flowers depend on one gene; in Drosophila, the gene that determines the white color of the eyes affects the lightening of body color and changes in some internal organs; In humans, the gene responsible for red hair also determines lighter skin color and the appearance of freckles. Marfan syndrome is caused by an autosomal dominant pleiotropic gene and is manifested by high growth, elongation of the bones of the fingers and toes (spider fingers), joint hypermobility, subluxation of the lens of the eye, and heart disease.

This multiple action is typical for most genes. However, one should not imagine that a pleiotropic gene influences each trait equally. The vast majority of genes with varying degrees of pleiotropy are characterized by a stronger effect on one trait and a much weaker effect on another.

Genotype as an integral system

The fact of splitting of hybrids in the offspring allows us to assert that the genotype is composed of individual elements - genes that can be inherited independently ( discreteness of the genotype). At the same time, the genotype cannot be considered as a simple mechanical sum of individual genes. A genotype is a system of interacting genes. More precisely, it is not the genes themselves (sections of DNA) that interact, but the gene products formed on their basis (RNA, and then proteins). Therefore, in some cases, the action of different genes is relatively independent, but, as a rule, the manifestation of a trait is the result of the interaction of products of different genes.

The genotype of any organism is a complex integral system of interacting genes. This integrity of the genotype arose historically in the process of evolution of the species. As a result of mutations, new genes constantly appear, new chromosomes and even new genomes are formed. Newly emerging genes can immediately interact with existing genes or modify the nature of their work, even being recessive, that is, without manifesting themselves.

Consequently, in each species of plants and animals the genotype manifests itself as an integral system that has historically developed at a given moment.

II. Consolidation of knowledge

Summarizing conversation while learning new material.

III. Homework

Study the textbook paragraph (relationship between genes and traits, types of interaction of allelic and non-allelic genes, pleiotropy, genotype as an integral system).

Solve the problems at the end of the textbook paragraph.

1. Complete dominance

2. Incomplete dominance - weakening of the effect of a dominant gene in the presence of a recessive one (in this case, heterozygotes exhibit an intermediate character of the trait)

3. Overdominance - a dominant gene in a heterozygous state is more pronounced than in a homozygous state

4. co-dominance - the genes of one allelic pair are equivalent and if both are present in the genotype, then both exert their effect (blood group IV)

5. interallelic complementation - a normal trait is formed as a result of the combination of two mutant genes in a heterozygote. The reason is that the products of recessive genes, interacting and complementing each other, form a trait identical to the activity of the dominant allele.

6. Allelic exclusion is a type of interaction in which one of the alleles of a gene is inactivated, which leads to the manifestation of different alleles in cells

10. Characteristics of the main types of interaction of non-allelic genes.

1. Complementarity- a type of interaction in which a new trait arises from the interaction of two dominant non-allelic genes located in the same genotype, whereas, being present separately in the genotype, they affect the trait in a different way.

Splits in F 2

2. Epistasis– suppression of alleles of one gene by the action of alleles of other genes.

The suppressing gene is called epistatic, the suppressed gene is called hypostatic.

Epistatic interaction of non-allelic genes can be dominant (13:3, 12:3:1) and recessive (9:3:4).

3. Polymerism– several dominant non-allelic genes determine the same trait. Such genes are designated by the same letters with different indices.

Polymeria happens:

Non-cumulative - it is not the number of dominant genes in the genotype that influences, but the presence of at least one (15:1)

Numerous experiments have confirmed the correctness of the patterns established by Mendel. At the same time, facts have emerged showing that the numerical relationships obtained by Mendel during the splitting of the hybrid generation were not always observed. This indicated that the relationships between genes and traits were more complex. It turned out that the same gene can influence the development of several traits; the same trait can develop under the influence of many genes.

It should be noted that the interaction of genes is of a biochemical nature, that is, it is not genes that interact with each other, but their products. The product of a eukaryotic gene can be either a polypeptide, tRNA, or rRNA.

TYPES OF INTERACTION OF ALLELIC GENES

There are complete dominance, incomplete dominance, codominance, and allelic exclusion.

Allelic genes are called genes located in identical loci of homologous chromosomes. A gene can have one, two, or more molecular forms. The appearance of the second and subsequent molecular forms is a consequence of gene mutation. If a gene has three or more molecular forms, it is said to be multiple allelism. Of the many molecular forms, only two can be present in one organism, which is explained by the pairing of chromosomes.

Complete Domination

Complete Domination- this is a type of interaction of allelic genes in which the phenotype of heterozygotes does not differ from the phenotype of homozygotes in terms of dominance, that is, the product of a dominant gene is present in the phenotype of heterozygotes. Complete dominance is widespread in nature and occurs during inheritance, for example, of the color and shape of pea seeds, eye color and hair color in humans, Rh antigen, and many others. etc.

The presence of the Rh antigen (Rh factor) of erythrocytes is determined by the dominant Rh gene. That is, the genotype of a Rh-positive person can be of two types: either RhRh or Rhrh; The genotype of a Rh negative person is rhrh. If, for example, the mother is Rh-negative, and the father is Rh-positive and heterozygous for this trait, then with this type of marriage, both Rh-positive and Rh-negative children can be born with equal probability.

An Rh conflict may occur between an Rh-positive fetus and an Rh-negative mother.

This is the name of the type of interaction of allelic genes in which the phenotype of heterozygotes differs from both the phenotype of dominant homozygotes and the phenotype of recessive homozygotes and has an average (intermediate) value between them. Occurs when inheriting the color of the perianth of the night beauty, snapdragon, color of the fur of guinea pigs, etc.

Mendel himself encountered incomplete dominance when he crossed a large-leaved pea variety with a small-leaved one. The first generation hybrids did not repeat the trait of any of the parent plants; they had medium-sized leaves.

When crossing homozygous red-fruited and white-fruited strawberry varieties, the entire first generation of hybrids has pink fruits. When crossing these hybrids with each other we get: by phenotype - 1/4 red-fruited, 2/4 pink-fruited and 1/4 white-fruited plants, by genotype - 1/4 AA, 1/2 Aa, 1/4 aa (and by phenotype, and by genotype the ratio is 1:2:1). The correspondence of segregation by genotype to segregation by phenotype is characteristic of incomplete dominance, since heterozygotes are phenotypically different from homozygotes.

Codominance

Codominance- a type of interaction of allelic genes in which the phenotype of heterozygotes differs from both the phenotype of dominant homozygotes and the phenotype of recessive homozygotes, and the heterozygote phenotype contains products of both genes. Occurs during the formation, for example, of the IV blood group system (AB0) in a person.

In order to imagine how the inheritance of blood groups occurs in humans, you can look at the birth of children with what blood group is possible from parents who have one blood group, the other a third, and are heterozygous for this trait.

Allelic exclusion

Allelic exclusion called the absence or inactivation of one of a pair of genes; in this case, the phenotype contains the product of another gene (hemizygosity, deletion, heterochromatization of the chromosome region in which the desired gene is located).

TYPES OF INTERACTION OF NON-ALLELIC GENES

Complementarity, epistasis, polymerization.

Non-allelic genes- genes located either in non-identical loci of homologous chromosomes, or in different pairs of homologous chromosomes.