Dominant and recessive genes. The dominant trait is

The type of inheritance usually refers to the inheritance of a particular trait depending on whether the gene (allele) that determines it is located on the autosomal or sex chromosome, and whether it is dominant or recessive. In this regard, the following main types of inheritance are distinguished: 1) autosomal dominant, 2) autosomal recessive, 3) sex-linked dominant inheritance and 3) sex-linked recessive inheritance. Of these, 4) sex-limited autosomal and 5) holandric types of inheritance are separately distinguished. In addition, there is 6) mitochondrial inheritance.

At autosomal dominant mode of inheritance the allele of the gene that determines the trait is located in one of the autosomes (non-sex chromosomes) and is dominant. This symptom will appear in all generations. Even when crossing genotypes Aa and aa, it will be observed in half of the offspring.

When autosomal recessive type a trait may not appear in some generations but appear in others. If the parents are heterozygotes (Aa), then they are carriers of a recessive allele, but have a dominant trait. When crossing Aa and Aa, ¾ of the offspring will have a dominant trait and ¼ will have a recessive trait. When crossing Aa and aa in ½, the recessive allele of the gene will manifest itself in half of the descendants.

Autosomal traits occur with equal frequency in both sexes.

Sex-linked dominant inheritance similar to autosomal dominant with one difference: in a sex whose sex chromosomes are the same (for example, XX in many animals is a female organism), the trait will appear twice as often as in a sex with different sex chromosomes (XY). This is due to the fact that if the gene allele is located on the X chromosome of the male body (and the partner does not have such an allele at all), then all daughters will have it, and none of the sons. If the owner of a sex-linked dominant trait is a female organism, then the probability of its transmission is the same to both sexes of descendants.

At sex-linked recessive mode of inheritance Generation skipping may also occur, as in the case of the autosomal recessive type. This is observed when female organisms can be heterozygotes for a given gene, and male organisms do not carry the recessive allele. When a female carrier is crossed with a healthy male, ½ of the sons will express the recessive gene, and ½ of the daughters will be carriers. In humans, hemophilia and color blindness are inherited this way. Fathers never pass the disease gene to their sons (as they only pass on the Y chromosome).

Autosomal, sex-limited mode of inheritance observed when the gene that determines the trait, although localized in the autosome, appears only in one of the sexes. For example, the sign of the amount of protein in milk appears only in females. It is not active in males. Inheritance is approximately the same as in a sex-linked recessive type. However, here the trait can be passed on from father to son.

Hollandic inheritance is associated with the localization of the gene under study on the sex Y chromosome. This trait, regardless of whether it is dominant or recessive, will appear in all sons and not in any daughter.

Mitochondria have their own genome, which determines the presence mitochondrial type of inheritance. Since only the mitochondria of the egg end up in the zygote, mitochondrial inheritance occurs only from mothers (both daughters and sons).

Lecture: Basic types of inheritance of traits in humans

Autosomal dominant the type of inheritance (Fig. 11.2) is characterized by the following features:

1) patients in each generation;

2) a sick child with sick parents;

4) inheritance goes vertically and horizontally;

5) probability of inheritance 100%, 75% and 50%.

It should be emphasized that the above signs of an autosomal dominant type of inheritance will appear only when complete dominance. This is how polydactyly (six-fingered feet), freckles, curly hair, brown eye color, etc. are inherited in humans. With incomplete dominance, hybrids will exhibit an intermediate form of inheritance. If the gene has incomplete penetrance, there may not be patients in every generation.

Autosomal recessive mode of inheritance(Fig. 11.2) is characterized by the following features:

3) get sick in equally men and women;

4) inheritance occurs predominantly horizontally;

5) probability of inheritance 25%, 50% and 100%.

Most often, the probability of inheriting a disease of an autosomal recessive type is 25%, since due to the severity of the disease such patients either do not survive to childbearing age,

or do not get married. This is how phenylketonuria, sickle cell anemia, blue eye color, etc. are inherited in humans.

Sex-linked recessive mode of inheritance(Fig. 11.3) is characterized by the following features:

1) patients are not in every generation;

2) at healthy parents sick child;

3) predominantly men are affected;

4) inheritance occurs mainly horizontally;

5) the probability of inheritance is 25% for all children and 50% for boys.

This is how hemophilia, color blindness, hereditary anemia, muscular dystrophy, etc. are inherited in humans.

Sex-linked dominant mode of inheritance(Fig. 11.4) is similar to autosomal dominant, except that the man passes this trait on to all his daughters (sons receive a Y chromosome from their father, they are healthy). An example of such a disease is a special form of rickets that is resistant to treatment with vitamin B.

Hollandic type of inheritance(Fig. 11.5) is characterized by the following features:

1) patients in all generations;

2) only men get sick;

3) a sick father has all his sons sick;

4) the probability of inheritance is 100% in boys.

Holandric characteristics are not significant in hereditary pathology person. According to the holandric type, men inherit ichthyosis (flaking of the skin), hypertrichosis (excessive hair growth on ears and external auditory canals), membranes between the toes, etc.

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Abstract on biology

Basic types of inheritance of traits

There are many types of inheritance of traits: direct, indirect and complex.

Direct inheritance. in which variants of traits are preserved unchanged from generation to generation - this is the simplest type of inheritance of traits. Direct inheritance is often observed in plants that reproduce vegetatively or produce seeds through self-pollination, less often during the reproduction of animals (within the same breed) or cross-pollination in plants (within the same variety or line).

– Direct inheritance during vegetative propagation of plants

Example 1. Chinatown roses are characterized by bright yellow flowers. When propagated vegetatively, cuttings of this variety always produce plants with bright yellow flowers.

Example 2. Some varieties of weeping willow are characterized by bright yellow shoots. During vegetative propagation, cuttings of these varieties always produce trees with a weeping crown and bright yellow shoots.

– Direct inheritance during self-pollination in plants

Example 1. Pea varieties with green seeds and white flowers, when self-pollinated, always produce green peas in their offspring, from which plants with white flowers grow.

Example 2. Tomato varieties with yellow oblong fruits, when self-pollinated, always produce seeds from which plants with yellow oblong fruits grow.

– Direct inheritance during the reproduction of purebred animals and cross-pollination of purebred plants

The type of inheritance is autosomal dominant. Types of inheritance of traits in humans

All characteristic features our body are manifested under the influence of genes. Sometimes only one gene is responsible for this, but more often it happens that several units of heredity are responsible for the manifestation of a particular trait.

It has already been scientifically proven that for a person the manifestation of such signs as skin color, hair, eyes, degree mental development, depends on the activity of many genes at once. This inheritance does not exactly obey Mendel’s laws, but goes far beyond it.

The study of human genetics is not only interesting, but also important from the point of view of understanding the inheritance of various hereditary diseases. Nowadays, it is becoming quite relevant for young couples to seek genetic counseling so that, after analyzing the pedigree of each spouse, one can confidently say that the child will be born healthy.

Types of inheritance of traits in humans

If you know how a particular trait is inherited, you can predict the likelihood of its manifestation in offspring. All traits in the body can be divided into dominant and recessive. The interaction between them is not that simple, and sometimes it is not enough to know which one belongs to which category.

Now in scientific world exist following types inheritance in humans:

Monogenic inheritance.
Polygenic.
Unconventional.

These types of inheritance, in turn, are also divided into certain varieties.

Monogenic inheritance is based on Mendel's first and second laws. Polygenic is based on the third law. This implies the inheritance of several genes, most often non-allelic.

Non-traditional inheritance does not obey the laws of heredity and is carried out according to its own rules, unknown to anyone.

Monogenic inheritance

This type of inheritance of traits in humans obeys Mendeleev's laws. Considering the fact that there are two alleles of each gene in the genotype, the interaction between the female and male genome is considered separately for each pair.

Based on this, the following types of inheritance are distinguished:

Autosomal dominant.
Autosomal recessive.
X-linked dominant inheritance.
X-linked recessive.
Holandric inheritance.

Each type of inheritance has its own characteristics and characteristics.

Signs of autosomal dominant inheritance

The autosomal dominant type of inheritance is the inheritance of predominant traits that are located in autosomes. Their phenotypic manifestations can vary greatly. For some, the symptom may be barely noticeable, but sometimes its manifestation is too intense.

The autosomal dominant type of inheritance has the following characteristics:

The disease symptom appears in every generation.
The number of sick and healthy people is approximately the same, their ratio is 1:1.
If children of sick parents are born healthy, then their children will be healthy.
The disease affects both boys and girls equally.
The disease is transmitted equally from men and women.
How stronger influence on reproductive functions, the greater the likelihood of various mutations occurring.
If both parents are sick, then the child, being born homozygous for this trait, is more seriously ill compared to a heterozygote.

All these characteristics are realized only under conditions of complete dominance. In this case, only the presence of one dominant gene will be sufficient for the manifestation of the trait. The autosomal dominant type of inheritance can be observed in humans when inheriting freckles, curly hair, brown eyes and many others.

Autosomal dominant traits

Most people who are carriers of an autosomal dominant pathological trait are heterozygotes for it. Numerous studies confirm that homozygotes for a dominant anomaly have more severe and severe manifestations compared to heterozygotes.

This type of inheritance in humans is characteristic not only of pathological traits, but also some completely normal ones are inherited this way.

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Among the normal characteristics with this type of inheritance are:

Curly hair.
Dark eyes.
Straight nose.
A hump on the bridge of the nose.
Baldness in early age in men.
Right-handedness.
The ability to roll the tongue into a tube.
Dimple on the chin.

Among the anomalies that have an autosomal dominant mode of inheritance, the most famous are the following:

Polyfingered, can be on both hands and feet.
Fusion of the tissues of the phalanges of the fingers.
Brachydactyly.
Marfan syndrome.
Myopia.

If dominance is incomplete, then the manifestation of the trait cannot be observed in every generation.

Autosomal recessive mode of inheritance

A trait with this type of inheritance can only appear if a homozygote for this pathology is formed. Such diseases are more severe because both alleles of one gene are defective.

The likelihood of manifestation of such signs increases in closely related marriages, therefore in many countries it is prohibited to enter into an alliance between relatives.

The main criteria for such inheritance include the following:

If both parents are healthy, but are carriers of a pathological gene, then the child will be sick.
The gender of the unborn child does not play any role in inheritance.
For one married couple, the risk of having a second child with the same pathology is 25%.
If you look at the pedigree, you can see a horizontal distribution of patients.
If both parents are sick, then all children will be born with the same pathology.
If one parent is sick and the other is a carrier of such a gene, then the probability of having a sick child is 50%

Many metabolic diseases are inherited according to this type.

Type of inheritance linked to the X chromosome

This inheritance can be either dominant or recessive. Signs of dominant inheritance include the following:

Both sexes can be affected, but women are 2 times more likely.
If a father is sick, then he can pass on the diseased gene only to his daughters, because the sons receive the Y chromosome from him.
A sick mother is equally likely to give this disease to children of both sexes.
The disease is more severe in men because they lack the second X chromosome.

If there is a recessive gene on the X chromosome, then inheritance has the following characteristics:

A sick child can also be born to phenotypically healthy parents.
Men are most often affected, and women are carriers of the diseased gene.
If the father is sick, then you don’t have to worry about the health of your sons; they cannot get a defective gene from him.
The probability of having a sick child in a carrier woman is 25% if we're talking about about boys, it rises to 50%.

This is how diseases such as hemophilia, color blindness, muscular dystrophy, Kallmann syndrome and some others are inherited.

Autosomal dominant diseases

For the manifestation of such diseases, the presence of one defective gene is sufficient, if it is dominant. Autosomal dominant diseases have some characteristics:

Currently, there are about 4,000 thousand such diseases.
Both sexes are affected equally.
Phenotypic demorphism is clearly manifested.
If a mutation of a dominant gene occurs in gametes, it will most likely appear in the first generation. It has already been proven that men have an increased risk of receiving such mutations with age, which means they can give their children such diseases.
The disease often manifests itself in all generations.

Inheritance of a defective gene for an autosomal dominant disease has nothing to do with the sex of the child or the degree of development of this disease in the parent.

Autosomal dominant diseases include:

Marfan syndrome.
Huntington's disease.
Neurofibromatosis.
Tuberous sclerosis.
Polycystic kidney disease and many others.

All of these diseases can manifest themselves in varying degrees in different patients.

Marfan syndrome

This disease is characterized by damage to connective tissue, and consequently, its functioning. Disproportionately long limbs with thin fingers suggest Marfan syndrome. The type of inheritance of this disease is autosomal dominant.

The following symptoms of this syndrome can be listed:

Thin build.
Long "spider" fingers.
Defects of the cardiovascular system.
The appearance of stretch marks on the skin for no apparent reason.
Some patients report pain in muscles and bones.
Early development of osteoarthritis.
Rachiocampsis.
Too flexible joints.
Possible speech impairment.
Visual impairment.

You can name the symptoms of this disease for a long time, but most of of which is associated with the skeletal system. The final diagnosis will be made after all examinations have been completed and characteristic signs are found in at least three organ systems.

It may be noted that some people do not show signs of the disease. childhood, but become obvious a little later.

Even now, when the level of medicine is quite high, it is impossible to completely cure Marfan syndrome. Using modern drugs and treatment technologies, it is possible to prolong the life of patients with this disorder and improve its quality.

The most important aspect of treatment is the prevention of the development of aortic aneurysm. Regular consultations with a cardiologist are required. In emergency cases, aortic transplant surgery is indicated.

Huntington's chorea

This disease also has an autosomal dominant mode of inheritance. It begins to appear from the age of 35-50 years. This is due to the progressive death of neurons. Clinically, the following signs can be identified:

Erratic movements combined with decreased tone.
Antisocial behavior.
Apathy and irritability.
Manifestation of schizophrenic type.
Mood swings.

Treatment is aimed only at eliminating or reducing symptoms. They use tranquilizers and neuroleptics. No treatment can stop the development of the disease, so death occurs approximately 15-17 years after the first symptoms appear.

Polygenic inheritance

Many signs and diseases have an autosomal dominant mode of inheritance. What this is is already clear, but in most cases it is not so simple. Very often, not one, but several genes are inherited simultaneously. They manifest themselves under specific environmental conditions.

A distinctive feature of this inheritance is the ability to enhance the individual effect of each gene. The main features of such inheritance include the following:

The more severe the disease, the greater the risk of developing this disease in relatives.
Many multifactorial traits affect a specific gender.
How large quantity relatives has this symptom, the higher the risk of this disease occurring in future descendants.

All considered types of inheritance belong to the classical variants, but, unfortunately, many signs and diseases cannot be explained because they belong to non-traditional inheritance.

When planning the birth of a baby, do not neglect visiting a genetic consultation. A competent specialist will help you understand your pedigree and assess the risk of having a child with disabilities.

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Dominant- * dominant * dominant a) suppressive, for example, D. trait of one of the parents in hybrids in relation to the alternative trait of the other parent; b) manifested alleles, for example, in the F1 hybrid, regardless of whether other alleles are present in the genome... ...

- (lat.) adj. from the next dominant; dominant, predominant; a dominant (dominant) trait is one of the parental traits that is more developed and predominates in the offspring, as opposed to a non-developing, suppressed trait... ...

dominant- ANIMAL EMBRYOLOGY DOMINANT – a suppressive allele and a corresponding trait, manifested in the phenotype of both homo and heterozygous organisms... General embryology: Terminological dictionary

DOMINANT- [cm. dominant] adj. from the next dominant; dominant, predominant (for example, D. sign) ...

dominant trait- vyraujantysis požymis statusas T sritis augalininkystė apibrėžtis Požymis, kuris dėl vyraujančiojo alelio veikimo pasireiškia heterozigotiniame individe. atitikmenys: engl. dominant character rus. dominant trait; dominant trait ryšiai… Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas

- (lat. recessus retreat) that of the parental characteristics that does not develop in the offspring of the first generation is suppressed, in contrast to the developed, predominant dominant trait; R. the sign usually appears in some... Dictionary foreign words Russian language

Complex sign complex p- Complex trait, complex trait * complex trait, folded trait * complex trait is a genetic trait that is not inherited strictly according to Mendel’s laws (dominant, recessive or sex-linked), but maybe during the formation of a phenotype... ... Genetics. encyclopedic Dictionary

RECESSIVE (trait)- [from lat. recessus retreat] that of the parental characteristics that does not develop in the offspring of the first generation is suppressed, in contrast to the developed, predominant dominant trait; R. sign usually appears in some... ... Psychomotorics: dictionary-reference book

Mendel's laws are a set of basic provisions concerning the mechanisms of transmission of hereditary characteristics from parent organisms to their descendants; these principles underlie classical genetics. Usually in Russian-language textbooks three laws are described,... ... Wikipedia

If the problem does not indicate which sign is dominant, Which one then recessive, it can be determined based on the following considerations:

If, when crossing two organisms with alternative characteristics, only one appears in their offspring, then it will be dominant.
If an organism exhibits cleavage in its offspring, it is heterozygous and therefore carries dominant trait.
If two parents, identical in phenotype, give birth to a child with a trait different from them, then the trait present in the original forms is dominant.

Problem 2-13

Crossing a polled (hornless) bull with horned cows resulted in polled and horned calves. The cows did not have polled animals in their pedigree. Which trait is dominant? What is the genotype of the parents and offspring?

In cows, all ancestors carried the same trait, which means they belong to a pure line and are homozygous.
The F 1 offspring is not uniform; therefore, one or more heterozygous individuals participated in the crossing. Since cows are homozygous, the bull is heterozygous.
Heterozygous organisms with complete dominance carry a dominant trait, therefore, polledness is such a trait.

Record of crossing

A - polled, and - horned.

The dominant sign is polled. The genotype of a bull is Aa, cows - aa, calves - Aa and aa.

Problem 2-14

Datura, which has purple flowers, produced 30 offspring with purple and 9 with white flowers during self-pollination. What conclusions can be drawn about the inheritance of flower color in plants of this species? What part of the F 1 progeny will not produce segregation during self-pollination?

Problem 2-15

When gray flies were crossed with each other, segregation was observed in their F 1 offspring. 1392 individuals were gray and 467 individuals - black. Which trait is dominant? Determine the genotypes of the parents.

Problem 2-16

Two black female mice were bred with a brown male. One female gave birth to 20 black and 17 brown offspring, and the other produced 33 black offspring. Which trait is dominant? What are the genotypes of parents and offspring?

Problem 2-17

An albino child was born to two healthy parents. The second child was normal. Does a dominant or recessive gene determine albinism? Determine the genotypes of parents and children.

Problem 2-18

When gray chickens were crossed with white chickens, all the offspring turned out to be gray. When this offspring was crossed again with whites, the result was 172 individuals, of which 85 were gray. Which trait is dominant? What are the genotypes of both forms and their offspring?

Problem 2-19

When normal fruit flies were crossed with each other, 25% of their offspring ended up with reduced eyes. The latter were crossed with the parental individuals and 37 flies with reduced and 39 with normal eyes were obtained. Determine the genotypes of the fruit flies crossed in both experiments.

Problem 2-20

At Petya and Sasha's Brown eyes, and their sister Masha has blue ones. The mother of these children is blue-eyed, although her parents had brown eyes. Which trait is dominant? What color is dad's eyes? Write the genotypes of all the listed individuals.

Two brown-eyed people (grandfather and grandmother) gave birth to a child who differs from them in phenotype, therefore, they are heterozygous and their genotype is Aa.
Heterozygotes carry a dominant trait, which means brown eye color (A), and blue-eyedness is determined by a recessive gene (a).
The genotype of the blue-eyed mother and daughter is aa, as they exhibit a recessive trait.
The genotype of the sons is Aa, because they are brown-eyed (A), and could only inherit the recessive gene a from their mother.
The father must be brown-eyed, because the sons could get dominant gene But only from him. He also carries the recessive a gene because he has a child with the aa genotype. Therefore, the father's genotype is Aa.

Marriage scheme

The genotype of the grandparents on the mother's side is Aa, mother and daughter - aa, father and sons - Aa. The dominant feature is brown eye color.

Problem 2-21

In one of the zoos in India, an albino tiger was born to a pair of tigers with normal coloring. Albino tigers are extremely rare. What actions should breeders take to get it as quickly as possible? maximum amount tiger cubs with this trait?

Problem 2-22

Male cockroaches resistant to DDT were crossed with females sensitive to this insecticide. In F 1, all individuals turned out to be resistant to DDT, and in F 2, a split occurred: 5768 resistant and 1919 sensitive. Which feature is dominant? What proportion of resistant individuals, when crossed with each other, will produce sensitive offspring?

Problem 2-23

A gray male was brought from a nursery to a laboratory with mice homozygous for the gray gene. All first generation hybrids were gray. All hybrid females of this generation were crossed with the same male and in the second generation a color split was obtained (gray mice, black mice) in a ratio of 7:1. Explain the results, assuming that color depends on one pair of alleles.

In the F 2 offspring there are mice with a trait different from the original individuals. This suggests that heterozygous organisms took part in the crossing. The initial females are homozygous according to the conditions of the problem, therefore, the male is heterozygous.
Gray color is a dominant trait, as it appears in a heterozygous male.
When crossing homozygous and heterozygous mice, half of the F 1 offspring will have the AA genotype and half will have the Aa genotype.
In the second generation, crossing a male with homozygous females from the first half will produce only gray pups, and crossing with heterozygous females will produce a splitting ratio of 3:1, i.e. the proportion of black mice in the F 2 offspring will be equal to: 1/2 · 1/4 = 1/8, where 1/2 is the probability that a male will be crossed with a heterozygous female (only in this case the birth of a black mouse is possible), and 1 /4 is the probability of obtaining such a descendant from this cross. Overall Probability V in this case equal to the product of the probabilities.

This satisfies the conditions of the problem. Segregation in a ratio different from Mendelian (3:1) is due to the fact that genetically heterogeneous females participated in the crossing.

Problem 2-24

Inheritance of the Rh factor is carried out according to the usual autosomal dominant pattern. An organism with a Rh-positive factor (Rh+) carries the dominant gene R, and an organism with a Rh-negative factor (Rh-) carries the recessive gene r. If a husband and wife are Rh positive, can their child be Rh negative?

Problem 2-25

The child is Rh positive. What Rh factor can parents have?

A trait, regardless of whether the genotype is homozygous or heterozygous for a given allele. A dominant trait is a trait controlled by a dominant allele.

The most important patterns of inheritance were discovered by G. Mendel in experiments on plants. But even before his discoveries, in mid-18th century century, botanists moved from observations of the inheritance of plant characteristics to its experimental study. In 1760 I.G.Kelreuter, who worked part of his life in Russia and was Russian academician, conducted a series of experiments to study the transmission of traits when crossing plants. In experiments with tobacco, dope and carnations, Koelreitor showed that after the transfer of pollen from one plant to the pistil of another, seeds are formed, from which descendant plants grow, often having characteristics intermediate between those of the parent plants. He also found that this result did not depend on which parent plant the pollen came from (i.e., the equality of “father” and “mother” in transmitting traits to offspring). Koelreuter's experiments demonstrated the existence of sex in plants.

But what is especially important is what Koelreuter introduced into science new method studying heredity - a method of artificial hybridization. When pollen is artificially transferred from a flower of one variety to the pistil of a flower of another variety, a plant is obtained that comes from two varieties at once. Such a plant is called a hybrid. In this case, the paternal plant is the one from which the pollen is taken, and the maternal plant is the one that was pollinated with this pollen and on which the hybrid seeds ripen. Plants grown from these seeds are called first-generation hybrids by scientists. Using this method, the French botanists O. Sarge and C. Naudin in the middle of the 19th century, working on the pumpkin family, discovered the phenomenon of dominance. By crossing plants of different varieties with different characteristics, they observed that in the first hybrid generation, often all descendants showed characteristics of only one of the parents. These characteristics, which seem to “defeat” the characteristics of the other parent, were called dominant (from the Latin dominantis - dominant). Sarget, Naudin and other scientists discovered that all first-generation hybrids are similar to each other. This observation later became known as the rule of uniformity of first-generation hybrids. In this case, hybrids receive some of their traits from one variety, and some from another. So the offspring received some of the dominant traits from the father, and some from the mother.

And what happens to the “suppressed” traits that do not appear in the first generation hybrids (later they were called recessive from the Latin recess - retreat). Do they disappear completely? It turns out not. If you cross hybrids of the first generation with each other, then their descendants, hybrids of the second generation, differ in their characteristics from each other. The emergence of such a variety of characters is called splitting. At the same time, some of the second generation hybrids have the same characteristics that the parents of the original varieties had and which did not appear in the first hybrid generation. Thus, these characteristics did not disappear, but were only “masked” by dominant characteristics. All these gradually accumulating facts required their own understanding. This is what was done in the works of Gregor Mendel.