What is complementary interaction of genes. Interaction of non-allelic genes: types and forms

Complementary is the type of interaction of non-allelic genes, in which the action of a gene from one allelic pair is complemented by the action of a gene from another allelic pair, as a result of which a qualitatively new trait is formed.

A classic example of this interaction is the inheritance of the comb shape in chickens. The following comb forms are encountered: leaf-shaped - the result of the interaction of two recessive non-allelic genes aabb; walnut - the result of the interaction of two dominant non-allelic genes A- B-; rose-shaped and pea-shaped - with genotypes A- bb and aaB- , respectively.

Another example is the inheritance of coat color in mice. Coloring is gray, white and black, and there is only one pigment - black. The formation of a particular coat color is based on the interaction of two pairs of non-allelic genes:

A – a gene that determines pigment synthesis;

a – a gene that does not determine pigment synthesis;

B – a gene that determines the uneven distribution of the pigment;

b – a gene that determines the uniform distribution of the pigment.

Examples of complementary interactions in humans: retinoblastoma and nephroblastoma are encoded by two pairs of non-allelic genes.

Possible splitting options in F 2 with complementary interaction: 9:3:4; 9:3:3:1; 9:7.

epistasis

Epistasis is a type of interaction of non-allelic genes in which the action of a gene from one allelic pair is suppressed by the action of a gene from another allelic pair.

There are two forms of epistasis - dominant and recessive. In dominant epistasis, the dominant gene acts as a suppressor gene (suppressor), while in recessive epistasis, the recessive gene acts.

An example of dominant epistasis is the inheritance of plumage color in chickens. Two pairs of non-allelic genes interact:

FROM- a gene that determines the color of plumage (usually variegated),

With- a gene that does not determine the color of plumage,

I - color suppression gene

i A gene that does not suppress coloring.

Splitting options in F 2: 12:3:1, 13:3.

In humans, an example of dominant epistasis is fermentopathy (enzymopathies) - diseases, which are based on insufficient production of one or another enzyme.

An example of recessive epistasis is the so-called "Bombay phenomenon": in a family of parents where the mother had the O blood type and the father had the A blood type, two daughters were born, of which one had the AB blood type. Scientists suggested that the mother had the IB gene in the genotype, but its effect was suppressed by two recessive epistatic dd genes.

Polymerism

Polymeria is a type of interaction of non-allelic genes, in which several non-allelic genes determine the same trait, enhancing its manifestation. This phenomenon is the opposite of pleiotropy. According to the type of polymer, quantitative traits are usually inherited, which is the reason for the wide variety of their manifestation in nature.

For example, the color of grains in wheat is determined by two pairs of non-allelic genes:

A 1

a 1 - a gene that does not determine the red color;

A 2 - the gene that determines the red color;

a 2 - a gene that does not determine the red color.

A 1 A 1 A 2 A 2 – genotype of plants with red grains;

a 1 a 1 a 2 a 2 - plant genotype with white colored grains.

Splitting in F 2: 15:1 or 1:4:6:4:1.

In humans, according to the type of polymer, traits such as height, hair color, skin color, blood pressure, and mental abilities are inherited.

Complementarity. Complementary (complementum - means of replenishment) are mutually complementary genes, when the formation of a trait requires the presence of several non-allelic (usually dominant) genes. This type of inheritance is widespread in nature.

Complementary interaction of non-allelic genes is characteristic of humans, for example, the process of forming gender. Sex determination in a person occurs at the time of fertilization, if the egg is fertilized by a sperm with an X chromosome, girls are born, if with Y, boys are born. It has been established that the Y chromosome determines the differentiation of the gonads according to the male type synthesizing the hormone testosterone and is not always able to ensure the development of the male organism. This requires a protein - a receptor, which is synthesized by a special gene present on another chromosome. This gene can mutate, and then an individual with the XY karyotype looks like a woman. These people cannot have offspring, tk. the sex glands - the testes - are underdeveloped, and the formation of the body often follows the female type, but the uterus and vagina are underdeveloped. it Morris syndrome or testicular feminization.

A typical example of complementarity is the development of hearing in humans. For normal hearing, the human genotype must contain dominant genes from different allelic pairs - D and E, where D is responsible for the normal development of the cochlea, and the E gene for the development of the auditory nerve. In recessive homozygotes (dd), the cochlea will be underdeveloped, and with its genotype, the auditory nerve will be underdeveloped. People with DDEE, DDEE, DDEE, DDEE genotypes will have normal hearing, while people with DDEE, DDEE, DDEE, DDEE genotypes will have no hearing.

epistasis- this is the interaction of non-allelic genes, opposite to the complementary one. There is an epistatic gene or an inhibitor gene that suppresses the action of both dominant and recessive non-allelic genes. Distinguish between dominant and recessive epistasis.

Dominant epistasis can be observed in the inheritance of plumage color in chickens.

C - pigment synthesis in feather.

c - lack of pigment in the feather.

J is an epistatic gene that suppresses the action of gene C.

j - does not suppress the action of gene C.

An example of recessive epistasis in humans is the "Bombay phenomenon" in the inheritance of blood types. It is described in a woman who received the allele J B (third blood group) from her mother, and phenotypically the woman has the first blood group. It was found that the activity of the J B allele is suppressed by a rare recessive allele of the x gene, which in the homozygous state has an epistatic effect (I B I B xx).

Polymerism- this is a phenomenon in which several dominant non-allelic genes determine (determine) one trait. The degree of manifestation of the trait depends on the number of dominant genes in the genotype. The more of them, the more pronounced the sign.

According to the type of polymer, skin color is inherited in humans.

S 1 S 2 - dark skin.

s 1 s 2 - light skin.

In the same way, many quantitative and qualitative traits are inherited in humans and animals: height, body weight, blood pressure, etc.

To a large extent, the manifestation of polygenic traits also depends on environmental conditions. A person may have a predisposition to various diseases: hypertension, obesity, diabetes mellitus, schizophrenia, etc. These signs, under favorable environmental conditions, may not appear or be mildly pronounced. This distinguishes polygenically inherited traits from monogenic ones. By changing environmental conditions and taking preventive measures, it is possible to significantly reduce the frequency and severity of some multifactorial diseases.

Pleiotropic action of the gene- This is the determination by one gene of several traits. The multiple action of the gene is due to the synthesis of different polypeptide chains of the protein, which affect the development of several unrelated features and properties of the organism. This phenomenon was first discovered by Mendel in plants with purple flowers, which always had a red color at the base of the leaf petiole, and the seed coat was brown. These three traits are determined by the action of one gene.

The pleiotropic effect of the gene can also be observed in Karakul sheep.

A is grey.

a - black color.

AA - gray color + anomaly in the structure of the stomach (absence of a scar), that is, individuals homozygous for the dominant gene die after birth.

In humans, the pleiotropic effect of the gene is observed when the disease is inherited - Marfan syndrome. In this case, one gene is responsible for the inheritance of several traits: subluxation of the lens of the eye, anomalies in the cardiovascular system, "spider fingers".

Independent work

A classic example of this interaction is the inheritance of the comb shape in chickens. The following comb forms are encountered: leaf-shaped - the result of the interaction of two recessive non-allelic genes aabb; walnut - the result of the interaction of two dominant non-allelic genes A-B-; rose-shaped and pea-shaped - with genotypes A-bb and aaB-, respectively.

A- a gene that determines pigment synthesis;

a - a gene that does not determine pigment synthesis;

B- a gene that determines the uneven distribution of the pigment;

b- a gene that determines the uniform distribution of the pigment.

Examples of complementary interactions in humans: retinoblastoma and nephroblastoma are encoded by two pairs of non-allelic genes.

Possible splitting options in F 2 with complementary interaction: 9:3:4; 9:3:3:1; 9:7.

epistasis

Epistasis is a type of interaction of non-allelic genes in which the action of a gene from one allelic pair is suppressed by the action of a gene from another allelic pair.

There are two forms of epistasis - dominant and recessive. In dominant epistasis, the dominant gene acts as a suppressor gene (suppressor), while in recessive epistasis, the recessive gene acts.

An example of dominant epistasis is the inheritance of plumage color in chickens. Two pairs of non-allelic genes interact:

FROM- a gene that determines the color of plumage (usually variegated),

With- a gene that does not determine the color of plumage,

I- color suppression gene

i A gene that does not suppress coloring.

Splitting options in F 2: 12:3:1, 13:3.

In humans, an example of dominant epistasis is fermentopathy (enzymopathies) - diseases, which are based on insufficient production of one or another enzyme.

Polymerism

For example, the color of grains in wheat is determined by two pairs of non-allelic genes:

A 1

a 1- a gene that does not determine the red color;

A2- the gene that determines the red color;

a 2- a gene that does not determine the red color.

A 1 A 1 A 2 A 2 – genotype of plants with red grains;

a 1 a 1 a 2 a 2 - plant genotype with white grains.

Splitting in F 2: 15:1 or 1:4:6:4:1.

In humans, according to the type of polymer, traits such as height, hair color, skin color, blood pressure, and mental abilities are inherited.

position effect

The position effect is a type of interaction of non-allelic genes, due to the position of the gene in the genotype.

Example - protein inheritance Rh- factor (Rh factor). 85% of Europeans have the Rh factor ( Rh+), 15% do not have it ( Rh-). The Rh factor is determined by three dominant genes (C, D, E) located next to each other on the chromosome.

Two people with the same CcDDEe genotype will have different phenotypes depending on the arrangement of allelic genes in a pair of homologous chromosomes: in variant A, there is a lot of E antigen, but little C antigen; in variant B, there is little antigen E, but a lot of antigen C.

Option A Option B

Now let us turn to the problem of the interaction of non-allelic genes. If the development of a trait is controlled by more than one pair of genes, then this means that it is under polygenic control. Several main types of gene interaction have been established: complementarity, epistasis, polymerization and pleiotropy.

The first case of non-allelic interaction was described as an example of a deviation from Mendel's laws by the English scientists W. Betson and R. Pennet in 1904 when studying the inheritance of the comb shape in chickens. Different breeds of chickens are characterized by different comb shapes. Wyandottes have a low, regular, papilla-covered crest, known as the "pink". Brahms and some fighting chickens have a narrow and high crest with three longitudinal elevations - “pea-shaped”. Leghorns have a simple or leaf-shaped crest, consisting of a single vertical plate. Hybridological analysis showed that the simple comb behaves as a completely recessive trait in relation to the rose and pea. The splitting in F 2 corresponds to the formula 3: 1. When crossing races with a rose-shaped and pea-shaped comb, hybrids of the first generation develop a completely new shape of the comb, resembling a half of a walnut kernel, in connection with which the comb was called "nut-shaped". When analyzing the second generation, it was found that the ratio of different forms of the crest in F 2 corresponds to the formula 9: 3: 3: 1, which indicated the dihybrid nature of the crossing. A crossover scheme was developed to explain the mechanism of inheritance of this trait.

Two non-allelic genes are involved in determining the shape of the crest in chickens. The dominant R gene controls the development of the pink crest, and the dominant P gene controls the development of the pisiform. The combination of recessive alleles of these rrpp genes causes the development of a simple crest. The walnut crest develops when both dominant genes are present in the genotype.

The inheritance of the crest shape in chickens can be attributed to the complementary interaction of non-allelic genes. Complementary, or additional, are genes that, when combined in the genotype in a homo- or heterozygous state, determine the development of a new trait. The action of each of the genes individually reproduces the trait of one of the parents.

Scheme illustrating the interaction of non-allelic genes,
determining the shape of the comb in chickens

The inheritance of the genes that determine the shape of the crest in chickens fits perfectly into the dihybrid cross scheme, since they behave independently during distribution. The difference from the usual dihybrid crossing is manifested only at the level of the phenotype and boils down to the following:

F 1 hybrids are not similar to either parent and have a new trait;
In F 2, two new phenotypic classes appear, which are the result of the interaction of either dominant (nut-shaped comb) or recessive (simple comb) alleles of two independent genes.

Mechanism complementary interaction studied in detail on the example of the inheritance of eye color in Drosophila. The red color of the eyes in wild-type flies is determined by the simultaneous synthesis of two pigments, brown and bright red, each of which is controlled by a dominant gene. Mutations affecting the structure of these genes block the synthesis of either one or the other pigment. Yes, a recessive mutation. brown(the gene is located on the 2nd chromosome) blocks the synthesis of a bright red pigment, and therefore the homozygotes for this mutation have brown eyes. recessive mutation scarlet(the gene is located on the 3rd chromosome) disrupts the synthesis of brown pigment, and therefore homozygotes stst have bright red eyes. With the simultaneous presence in the genotype of both mutant genes in the homozygous state, both pigments are not produced and the eyes of the flies are white.

In the described examples of complementary interaction of non-allelic genes, the phenotype splitting formula in F 2 corresponds to 9: 3: 3: 1. Such splitting is observed if the interacting genes individually have an unequal phenotypic manifestation and it does not coincide with the phenotype of the homozygous recessive. If this condition is not met, other ratios of phenotypes take place in F 2 .

For example, when two varieties of figured pumpkin with a spherical fruit are crossed, the hybrids of the first generation have a new feature - flat or disc-shaped fruits. When hybrids are crossed with each other in F 2, splitting is observed in the ratio of 9 disc-shaped: 6 spherical: 1 elongated.

Analysis of the scheme shows that two non-allelic genes with the same phenotypic manifestation (spherical shape) are involved in determining the shape of the fetus. The interaction of the dominant alleles of these genes gives a disc-shaped form, the interaction of recessive alleles - an elongated one.

Another example of complementary interaction is the inheritance of coat color in mice. The wild gray coloration is determined by the interaction of two dominant genes. Gene BUT responsible for the presence of the pigment, and the gene AT for its uneven distribution. If only the gene is present in the genotype BUT (A-bb), then the mice are uniformly colored black. If only the gene is present AT (aaB-), then the pigment is not produced and the mice are unstained, as is the homozygous recessive aabb. This action of the genes leads to the fact that in F 2 the splitting according to the phenotype corresponds to the formula 9: 3: 4.

	AB	Ab	aB	ab
AB	AABB ser.	AABb ser.	AaBB ser.	AaBb ser.
Ab	AABb ser.	AAbb black	AaBb ser.	Aabb black
aB	AaBB ser.	AaBb ser.	aaBB white	aaBb white
ab	AaBb ser.	Aabb black	aaBb white	aabb white

F 2: 9 Ser. : 3 black : 4 Bel.

A complementary interaction has also been described in the inheritance of flower color in sweet peas. Most of the varieties of this plant have purple flowers with purple wings, which are characteristic of the wild Sicilian race, but there are also varieties with a white color. By crossing plants with purple flowers with plants with white flowers, Betsson and Pennet found that the purple color of the flowers completely dominates the white, and in F 2 there is a ratio of 3: 1. But in one case, from crossing two white plants, offspring were obtained, consisting only of plants with colored flowers. During self-pollination of F 1 plants, offspring were obtained, consisting of two phenotypic classes: with colored and uncolored flowers in the ratio 9/16: 7/16.

The results obtained are explained by the complementary interaction of two pairs of non-allelic genes, the dominant alleles of which ( FROM and R) individually are not able to provide the development of purple color, as well as their recessive alleles ( ssrr). Coloring appears only if both dominant genes are present in the genotype, the interaction of which ensures the synthesis of the pigment.

purple
F2

	CP	cp	cP	cp
CP	CCPP purple	CCPp purple	CCPP purple	CcPp purple
cp	CCPp purple	CCpp white	CcPp purple	ccpp white
cP	CCPP purple	CcPp purple	ccPP white	ccPp white
cp	CcPp purple	ccpp white	ccPp white

F 2: 9 magenta : 7 Bel.

In the given example, the splitting formula in F 2 - 9: 7 is due to the absence of their own phenotypic manifestation in the dominant alleles of both genes. However, the same result is also obtained if the interacting dominant genes have the same phenotypic expression. For example, when crossing two varieties of corn with purple grains in F 1, all hybrids have yellow grains, and in F 2 there is a splitting of 9/16 yellow. : 7/16 fiol.

epistasis- another type of non-allelic interaction, in which the suppression of the action of one gene by another non-allelic gene occurs. A gene that prevents the expression of another gene is called epistatic, or a suppressor, and one whose action is suppressed is called hypostatic. Both a dominant and a recessive gene can act as an epistatic gene (respectively, dominant and recessive epistasis).

An example of dominant epistasis is the inheritance of coat color in horses and fruit color in pumpkins. The inheritance pattern of these two traits is exactly the same.

	CB	Cb	cB	cb
CB	CCBB ser.	CCBB ser.	CCBB ser.	CcBb ser.
Cb	CCBb ser.	CCbb ser.	CcBb ser.	ccbb ser.
cB	CCBB ser.	CcBb ser.	ccBB black	ccBb black
cb	CcBb ser.	ccbb ser.	ccBb black	ccbb red

F 2: 12 Ser. : 3 black : 1 red

The scheme shows that the dominant gene for gray color FROM is epistatic with respect to the dominant gene AT, which causes the black color. In the presence of a gene FROM gene AT does not show its effect, and therefore F 1 hybrids carry a trait determined by the epistatic gene. In F 2, the class with both dominant genes merges in phenotype (gray color) with the class in which only the epistatic gene is present (12/16). Black color appears in 3/16 hybrid offspring, in the genotype of which there is no epistatic gene. In the case of a homozygous recessive, the absence of a suppressor gene allows the recessive c gene to appear, which causes the development of a red color.

Dominant epistasis has also been described in the inheritance of feather color in chickens. The white color of the plumage in Leghorn chickens dominates over the colored black, pockmarked and other colored breeds. However, the white coloration of other breeds (such as Plymouth Rocks) is recessive in relation to colored plumage. Crosses between individuals with a dominant white color and individuals with a recessive white color in F 1 produce white offspring. In F 2, splitting is observed in a ratio of 13: 3.

An analysis of the scheme shows that two pairs of non-allelic genes are involved in determining feather color in chickens. Dominant gene of one pair ( I) is epistatic with respect to the dominant gene of the other pair, causing color development ( C). In this regard, only those individuals whose genotype contains the gene FROM, but no epistatic gene I. In recessive homozygotes ccii they lack an epistatic gene, but they do not have a gene that provides pigment production ( C), so they are white in color.

As an example recessive epistasis you can consider the situation with the albinism gene in animals (see above for the inheritance pattern of coat color in mice). The presence in the genotype of two alleles of the albinism gene ( aa) does not allow the dominant color gene to appear ( B) — genotypes aaB-.

Polymer type of interaction was first established by G. Nielsen-Ehle while studying the inheritance of grain color in wheat. When crossing a red-grain wheat variety with a white-grain one in the first generation, the hybrids were colored, but the color was pink. In the second generation, only 1/16 of the offspring had a red grain color and 1/16 - white, the rest had an intermediate color with varying degrees of expression of the trait (from pale pink to dark pink). The analysis of splitting in F 2 showed that two pairs of non-allelic genes are involved in determining the color of the grain, the action of which is summed up. The severity of the red color depends on the number of dominant genes in the genotype.

Polymeric genes are usually denoted by the same letters with the addition of indices, in accordance with the number of non-allelic genes.

The action of dominant genes in this crossing is additive, since the addition of any of them enhances the development of the trait.

	A 1 A 2	A 1 a 2	a 1 A 2	a 1 a 2
A 1 A 2	A 1 A 1 A 2 A 2 red	A 1 A 1 A 2 Aa 2 bright pink.	A 1 a 1 A 2 A 2 bright pink.	A 1 a 1 A 2 a 2 pink
A 1 a 2	A 1 A 1 A 2 a 2 bright pink.	A 1 A 1 a 2 a 2 pink	A 1 a 1 A 2 a 2 pink	A 1 a 1 a 2 a 2 pale pink.
a 1 A 2	A 1 a 1 A 2 A 2 bright pink.	A 1 a 1 A 2 a 2 pink	a 1 a 1 A 2 A 2 pink	a 1 a 1 A 2 a 2 pale pink.
a 1 a 2	A 1 a 1 A 2 a 2 pink	A 1 a 1 a 2 a 2 pale pink.	a 1 a 1 A 2 a 2 pale pink.	a 1 a 1 a 2 a 2 white

F 2: 15 color : 1 Bel.

The described type of polymerization, in which the degree of development of a trait depends on the dose of the dominant gene, is called cumulative. Such a pattern of inheritance is common for quantitative traits, which should also include color, because its intensity is determined by the amount of pigment produced. If we do not take into account the degree of expression of color, then the ratio of colored and uncolored plants in F 2 corresponds to the formula 15: 1.

However, in some cases, polymerization is not accompanied by a cumulative effect. An example is the inheritance of the form of seeds in a shepherd's purse. Crossing of two races, one of which has triangular fruits, and the other ovoid, gives in the first generation hybrids with a triangular fruit shape, and in the second generation, splitting according to these two characters is observed in the ratio of 15 triangles. : 1 eggs.

This case of inheritance differs from the previous one only at the phenotypic level: the absence of a cumulative effect with an increase in the dose of dominant genes determines the same severity of the trait (triangular shape of the fetus), regardless of their number in the genotype.

The interaction of non-allelic genes also includes the phenomenon pleiotropy- multiple action of the gene, its influence on the development of several traits. The pleiotropic effect of genes is the result of a serious metabolic disorder due to the mutant structure of this gene.

For example, Irish cows of the Dexter breed differ from the closely related Kerry breed by shortened legs and head, but at the same time by better meat qualities and fattening ability. When crossing cows and bulls of the Dexter breed, 25% of the calves have signs of the Kerry breed, 50% are similar to the Dexter breed, and in the remaining 25% of cases, miscarriages of ugly bulldog calves are observed. Genetic analysis made it possible to establish that the cause of the death of some of the offspring is the transition to the homozygous state of a dominant mutation that causes underdevelopment of the pituitary gland. In the heterozygote, this gene leads to the appearance of dominant traits of short legs, short head and increased ability to deposit fat. In the homozygote, this gene has a lethal effect, i.e. in relation to the death of offspring, it behaves like a recessive gene.

The lethal effect upon transition to the homozygous state is characteristic of many pleiotropic mutations. Thus, in foxes, dominant genes that control the platinum and white-faced fur colors, which do not have a lethal effect in the heterozygote, cause the death of homozygous embryos at an early stage of development. A similar situation occurs with the inheritance of gray wool color in Shirazi sheep and underdevelopment of scales in mirror carp. The lethal effect of mutations leads to the fact that animals of these breeds can only be heterozygous and, when interbreeding, they give splitting in the ratio of 2 mutants: 1 norm.

F1
F 1: 2 boards : 1 black

However, most lethal genes are recessive, and individuals heterozygous for them have a normal phenotype. The presence of such genes in the parents can be judged by the appearance in the offspring of homozygous freaks, abortions and stillborns. Most often, this is observed in closely related crosses, where parents have similar genotypes, and the chances of passing harmful mutations into a homozygous state are quite high.

Pleiotropic genes with a lethal effect are found in Drosophila. Yes, dominant genes Curly- upturned wings star- starry eyes Notch— the jagged edge of the wing and a number of others in the homozygous state cause the death of flies in the early stages of development.

Known recessive mutation white, first discovered and studied by T. Morgan, also has a pleiotropic effect. In the homozygous state, this gene blocks the synthesis of eye pigments (white eyes), reduces the viability and fertility of flies, and alters the shape of the testes in males.

In humans, an example of pleiotropy is Marfan's disease (spider finger syndrome, or arachnodactyly), which is caused by a dominant gene that causes increased finger growth. At the same time, it determines the anomalies of the lens of the eye and heart disease. The disease occurs against the background of an increase in intelligence, in connection with which it is called the disease of great people. A. Lincoln, N. Paganini suffered from it.

The pleiotropic effect of the gene, apparently, underlies the correlative variability, in which a change in one trait entails a change in others.

The interaction of non-allelic genes should also include the influence of modifier genes, which weaken or enhance the function of the main structural gene that controls the development of the trait. In Drosophila, modifier genes are known that modify the process of wing venation. At least three modifier genes are known that affect the amount of red pigment in the hair of cattle, as a result of which the coat color in different breeds ranges from cherry to fawn. In humans, modifier genes change the color of the eyes, increasing or decreasing its intensity. Their action explains the different color of the eyes in one person.

The existence of the phenomenon of gene interaction has led to the emergence of such concepts as “genotypic environment” and “gene balance”. Under the genotypic environment is meant the environment in which the newly emerging mutation falls, i.e. the whole complex of genes present in a given genotype. The concept of “gene balance” refers to the ratio and interaction between genes that affect the development of a trait. Usually, genes are designated by the name of the trait that occurs when a mutation occurs. In fact, the manifestation of this feature is often the result of a violation of the function of the gene under the influence of other genes (suppressors, modifiers, etc.). The more complex the genetic control of a trait, the more genes involved in its development, the higher the hereditary variability, since the mutation of any gene disrupts the gene balance and leads to a change in the trait. Consequently, for the normal development of an individual, not only the presence of genes in the genotype is necessary, but also the implementation of the entire complex of inter-allelic and non-allelic interactions.

Another type of interaction of non-allelic genes is complementarity. It lies in the fact that the development of a trait requires the presence in the genotype of dominant alleles of two specific genes. A classic example of complementary gene interaction is the inheritance of the color of sweet pea corolla petals. When white flowers are crossed, the offspring have a new trait - red corolla petals, and in the second generation the splitting is 9 red to 7 white.

M - chromogen N - chromogenase

m - absence n - absence

R: ♀ ММnn ´ ♂ mmNN

white white

genotype: diheterozygous

phenotype: purplish red

P: ♀ MnNn ´ ♂ MmNn

F 2: Punnett

♀ ♂	MN	Mn	mN	mn
MN	MMNN	MMNn	MmNN	MmNn
Mn	MMNn	MMnn	MmNn	mmn
mN	MmNN	MmNn	mmNN	mmNn
mn	MmNn	mmn	mmNn	mmnn

by genotype: 1: 2: 2: 1: 4: 1: 2: 2: 1

by phenotype: 9:7

purple red white

Thus, with the complementary interaction of genes, a deviation from the law of independent inheritance is also observed.

In humans, hair pigmentation genes have a complementary effect:

m 1 - a significant amount of melanin

m 2 - the average amount of melanin

m 3 - a small amount of melanin

R - red pigment

r - no pigment

The combination of alleles of these genes gives the whole spectrum of hair colors. The degree of dominance is as follows: tm 1 >m 2 >R>m 1 >r

Genotypes: Phenotype:

m 1 m 1 RR brunette (with gloss)

m 1 m 1 Rr brunette (shiny hair)

m 1 m 1 rr brunette

m 1 m 2 RR dark brown

m 1 m 3 rr brown

m 2 m 2 Rr chestnut

m 2 m 2 RR auburn

М 2 m 3 RR auburn

m 3 m 3 RR bright red

m 3 m 3 Rr blond with a reddish tint

m 3 m 3 rr blond

Another example of complementary interaction is the production of an antiviral substance, interferon, by human cells. Its synthesis depends on the presence in the genotype of two dominant genes from different allelic pairs:

Phenotypic radical: Phenotype:

A-B - interferon is synthesized

aaB - interferon is not synthesized

A-BB interferon is not synthesized

aavv interferon is not synthesized

The inheritance of normal hemoglobin depends on 4 dominant genes from different allelic pairs. Only with the phenotypic radical A-B-C-D- hemoglobin binds to O 2 (oxyhemoglobin) and to CO 2 (carboxyhemoglobin). With all other combinations of genes somehow.

Portal for the student. Self-training

epistasis

Polymerism

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