What does a mutation in a heterozygous state mean. What is homozygous mutation

Date of: 03.03.2020

HETEROZYGOTE HETEROZYGOTE

(from hetero ... and zygote), an organism (cell), in which homologous chromosomes are decomp. alleles (alternative forms) of a particular gene. Heterozygosity, as a rule, determines the high viability of organisms, their good adaptability to changing environmental conditions, and therefore is widespread in natural populations. In experiments, G. is obtained by crossing homozygotes for dec. alleles. The offspring of such a cross are heterozygous for this gene. An analysis of the characteristics of G. in comparison with the original homozygotes allows us to conclude about the nature of the interaction decomp. alleles of one gene (complete or incomplete dominance, code ination, interallelic complementation). Some alleles determined. genes can only be in a heterozygous state (recessive lethal mutations, dominant mutations with a recessive lethal effect). Heterozygosity for various lethal factors in decomp. homologous chromosomes leads to the fact that the offspring of G. is represented by the same G. This phenomenon is the so-called. balanced mortality can serve, in particular, as the basis for "fixing" the effect of heterosis, which has great importance in s.-x. practice, but is “lost” in a number of generations due to the appearance of homozygotes. The average person has approx. 20% of the genes are in a heterozygous state. Determination of heterozygosity for recessive alleles that cause hereditary diseases(i.e., identifying carriers of this disease) is an important problem for honey. genetics. The term "G." they are also used for chromosomal rearrangements (they speak of G. by inversion, translocation, etc.). In the case of multiple allelism, the term “compound” is sometimes used for G. (from the English compound - complex, compound). For example, in the presence of the “normal” allele A and mutant a1 and a2, the a1/a2 heterozygote is called. compound in contrast to heterozygotes A/a1 or A/a2. (see HOMOZYGOTE).

.(Source: Biological encyclopedic Dictionary." Ch. ed. M. S. Gilyarov; Editorial: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected. - M.: Sov. Encyclopedia, 1986.)

heterozygote

A cell or individual in which two genes that determine a trait are different. That is, allelic genes ( alleles) - paternal and maternal - are not the same. For example, in the experiments of G. mendel for crossing pea varieties with different seed colors, homozygous individuals for the dominant gene of yellow color were used as parents ( A) and homozygous individuals for the recessive green gene ( A). All obtained hybrids of the first generation had a hereditary structure Ah, i.e. were heterozygotes. They had seeds yellow color as in homozygotes for the dominant gene.
Comparison of the traits of heterozygous individuals with the traits of homozygous parents makes it possible to study various forms of interaction between alleles of one gene (the nature of dominance, etc.). In general, heterozygosity provides organisms with greater viability and adaptability than homozygosity. Compare Homozygote.

.(Source: "Biology. Modern Illustrated Encyclopedia." Editor-in-Chief A.P. Gorkin; M.: Rosmen, 2006.)

Synonyms:

See what "HETEROZYGOTE" is in other dictionaries:

Heterozygous ... Spelling Dictionary

- (from hetero ... and zygote), a cell or organism in which homologous (paired) chromosomes carry different forms (alleles) of a particular gene. As a rule, it is a consequence of the sexual process (one of the alleles is introduced by the egg, and the other ... ... Modern Encyclopedia

- (from hetero ... and zygote) a cell or organism in which homologous chromosomes carry different forms (alleles) of a particular gene. Wed Homozygous ... Big Encyclopedic Dictionary

HETEROZYGOTE An organism that has two contrasting forms (ALLELES) of a GENE in a pair of CHROMOSOMES. In cases where one of the forms is DOMINANT, and the other is only recessive, the dominant form is expressed in the phenotype. see also HOMOZYGOTE ... Scientific and technical encyclopedic dictionary

In genetics, like any other science, there is a specific terminology designed to clarify key concepts. Back in school, many of us heard such terms as dominance, recessiveness, gene, allele, homozygosity and heterozygosity, but did not fully understand what was behind them. Let us analyze in more detail what a homozygote is, how it differs from a heterozygote, and what role allelic genes play in its formation.

Some common genetics

To answer the question of what a homozygote is, let's recall the experiments of Gregor Mendel. By crossing pea plants of different color and shape, he came to the conclusion that the resulting plant somehow inherits genetic information from its "ancestors". Although the concept of "gene" did not yet exist, Mendel managed to in general terms explain the mechanism of inheritance of traits. From the laws discovered by Mendel in the middle of the 19th century, the following statement followed, later called the "gamete purity hypothesis": "When a gamete is formed, only one of the two allelic genes responsible for a given trait enters it." That is, from each of the parents we receive only one allelic gene responsible for a certain trait - height, hair color, eye color, nose shape, skin tone.

Allelic genes can be dominant or recessive. This brings us very close to the definition of what a homozygote is. Dominant alleles are able to mask the recessive so that it does not manifest itself in the phenotype. If both genes are recessive or dominant in the genotype, then this is a homozygous organism.

Types of homozygotes

From the foregoing, one can answer the question of what a homozygote is: it is a cell in which the allelic genes responsible for a certain trait are the same. Allelic genes are located on homologous chromosomes and in the case of homozygotes can be either recessive (aa) or dominant (AA). If one allele is dominant and the other is not, then this is a heterozygote (Aa). In the case when the cell genotype is aa, then this is a recessive homozygous, if AA is dominant, since it carries alleles responsible for the dominant trait.

Crossing features

When crossing two identical (recessive or dominant) homozygotes, a homozygote is also formed.

For example, there are two white rhododendron flowers with bb genotypes. After crossing them, we will also get a white flower with the same genotype.

You can also give an example with the color of the eyes. If both parents have brown eyes and are homozygous for this trait, then their genotype is AA. Then all the children will have brown eyes.

However, crossing homozygotes does not always lead to the formation of an organism homozygous for any trait. For example, crossing red (DD) and white (dd) carnations can result in a pink or red-white flower. The pink carnation, like the two-tone one, is an example of incomplete dominance. In both cases, the resulting plants will be heterozygous with the Dd genotype.

Examples of homozygotes

There are quite a few examples of homozygotes in nature. White tulips, carnations, rhododendrons are all examples of recessive homozygotes.

In humans, as a result of the interaction of allelic genes, organisms that are homozygous for some trait are also often formed, whether it is very fair skin, Blue eyes, blonde hair or color blindness.

Dominant homozygotes are also common, however, due to the ability of dominant traits to mask recessive ones, it is impossible to immediately say whether a person is a carrier of a recessive allele or not. Most of the genes responsible for genetic diseases, are caused by gene mutations and are recessive, therefore they appear only if there is no normal, dominant allele on the homologous chromosomes.

is it possible to give birth healthy child if the mother has a mutation in the MTHFR gene? and got the best answer

Answer from Nightbird[guru]
A mother's mutation in the MTHFR gene is NOT a SENTENCE.
There may be mutations in different places, by the way.
When a mutant MTHFR gene is detected in a heterozygous state*, there are no good reasons for fear. As a preventive measure for hypercoagulable conditions, it is recommended to take folic acid 0.4 mg / day in two doses daily during pregnancy, eat well and examine the hemostasiogram once every three months (or according to indications).
The most common enzyme defect that is associated with a moderate increase in HC (homocysteine) levels is a mutation in the gene encoding MTHFR. MTHFR catalyzes the transition folic acid in her active form. To date, 9 mutations of the MTHFR gene located at the 1p36.3 locus have been described. The most common of these is the C677T substitution (in the MTHFR protein - the substitution of alanine for valine), which is manifested by thermolability and a decrease in the activity of the MTHFR enzyme. It has been observed that an increase in the content of folate in food can prevent an increase in the concentration of HC in plasma.
An increase in the level of homocysteine in the blood plasma directly correlates with the inhibition of thrombomodulin synthesis, a decrease in the activity of AT-III and endogenous heparin, and also with the activation of the production of thromboxane A2. In the future, such changes cause microthrombosis and microcirculation disorders, which, in turn, play a significant role in the pathology of the spiral arteries and the development of obstetric complications associated with changes in uteroplacental circulation.
The reason for the elevated blood homocysteine level: C677T variant in the MTHFR gene is a mutation in the gene for the enzyme methylenetetrahydrofolate reductase.
The replacement of cytosine with thymine at position 677 leads to a decrease in the functional activity of the enzyme to 35% of the average value.
Polymorphism data:
*frequency of occurrence of homozygotes in the population - 10-12%
* frequency of occurrence of heterozygotes in the population - 40%
....
Carriers of the T variant are deficient in folic acid during pregnancy, leading to neural tube defects in the fetus.
Smoking exacerbates the effects of the 677T variant....
The appointment of folic acid can significantly reduce the risk of the consequences of this variant of the polymorphism.
more details here --
In general, who will be taken where ... It is impossible to say for sure. It also depends on the father - what is in his genome !!!
Try asking your question in more detail here --
Or even better here --
GOOD LUCK!

(from lat. recessus - retreat, removal)

one of the forms of phenotypic expression of genes. When crossing individuals that differ in a certain trait, G. Mendel found that in hybrids of the first generation, one of the parental traits disappears (recessive), and the other appears (dominant) (see Mendelism, Mendel's laws). The dominant form (allele (See Alleles)) of the gene (A) manifests its effect in homo- and heterozygous states (AA, Aa), while the recessive allele (a) can appear only in the absence of the dominant (-a) (see Heterozygosity, homozygosity). That. , a recessive allele is a repressed member of an allelic pair of genes. Dominance or R. alleles are revealed only during the interaction of a specific pair of allelic genes. This can be traced when analyzing a gene that occurs in several states (the so-called multiple allele series). A rabbit, for example, has a series of 4 genes that determine the color of the coat (C - solid color, or agouti; cch - chinchilla; ch - Himalayan color; c - albino). If the rabbit has the Ccch genotype, then in this combination cch is a recessive allele, and in combinations cchch and cchc it dominates, causing the color of the chinchilla.

The nature of the manifestation of a recessive trait may change under the influence of external conditions. So, Drosophila has a recessive mutation (See Mutations) - “rudimentary wings”, which in the homozygous at the optimum temperature (25 ° C) leads to a sharp decrease in the size of the wings. When the temperature rises to 30 ° C, the size of the wings increases and can reach the norm, i.e., appear as a dominant trait.

The recessive effect of a gene may be due to a slowdown or change in the course of any biochemical function. A significant part of congenital metabolic disorders in humans is inherited according to a recessive type, i.e. clinical picture disease is observed only in homozygotes. In heterozygotes, the disease does not manifest itself due to the functioning of the normal (dominant) allele (see "Molecular diseases", Hereditary diseases). Most recessive lethal mutations are associated with a violation of vital biochemical processes, which leads to the death of individuals homozygous for this gene. Therefore, in the practice of livestock and crop production, it is important to identify individuals that carry recessive lethal and semi-lethal mutations so as not to involve harmful genes in the selection process. The effect of inbreeding depression during inbreeding (see Inbreeding) is associated with the transition of harmful recessive genes to the homozygous state and the manifestation of their action. At the same time, in breeding practice, recessive mutations often serve as valuable starting material. Thus, their use in breeding minks made it possible to obtain animals with skins of platinum, sapphire and other colors, which are often valued more than wild-type dark brown minks.

When conducting genetic analysis, a hybrid is crossed with parent form homozygous for recessive alleles. So it is possible to find out hetero- or homozygosity for the analyzed pairs of genes. Recessive mutations play an important role in the evolutionary process. The Soviet geneticist S. S. Chetverikov showed (1926) that natural populations contain a huge number of various recessive mutations in the heterozygous state. Wed Dominance, Codominance.

What is there to say? ? Only in the homozygote does it manifest itself when both chromosomes with this recessive trait meet ... In heterozygotes of his generations, the dominant "strangles" until both recessives meet.

Homozygous mutation MTHFR (C677 T) (note to self)

677T mutation and other pregnancy complications

Women with the 677TT genotype are prone to developing a vitamin deficiency in folic acid. In non-pregnant women homozygous for this allele, folate deficiency may be found only in erythrocytes, and plasma folate levels may not be affected. However, during pregnancy in homozygous women, there is a decrease in the concentration of folates not only inside the erythrocytes, but also in the blood plasma.

Studies have shown an increased risk of developing nephropathy in pregnant women with vascular diseases. This is in good agreement with data on the effect of high concentrations of homocysteine in the blood with the risk of developing nephropathy in pregnant women. In addition, it has been shown that the concentration of homocysteine in the blood correlates with the concentration of fibronectin in cells, which indicates an important role of homocysteine in the development of endothelial dysfunction during pregnancy. An increase in the frequency of the 677T allele was noted not only in late toxicosis (preeclampsia), but also in other pregnancy complications (placental abruption, fetal growth retardation, antenatal fetal death). The combination of the 677T allele with other risk factors leads to an increased risk early miscarriage. Adding folic acid to the diet significantly reduces the risk of pregnancy complications. The prophylactic value of adding folic acid to the diet is especially pronounced in the presence of hyperhomocysteinemia.

Thank you! I just have the mutation MTHFR (C677 T) - TT

Homocysteine was greatly elevated. For a year she took angiovit, Omega-3, chimes. A year later, homocysteine is normal.

Excellent article! Very well written!

Handed over for mutation? And homocysteine?

Year? Wow! I was prescribed angiovit for a month - my homocysteine is 9.776 (4.6 - 8.1). So I have such a mutation .. I read a lot. horror..

yes, I wrote homocysteine above, and mutations - I have just this case: (when T / T, i.e. homozygous mutation (((

And my homocysteine was 17. I went to OTTO to see a hematologist. She told me to take it all the time before pregnancy. And how to get pregnant immediately to her. In general, all your life you need to monitor the level of homocysteine and take these drugs from time to time. Here.

did they say anything about breeding? I just already had one ZB

I also have a mutation in other genes. The doctor said that she thinks that I can’t get pregnant because of this, and it seems to affect the gestation. She said that the blood becomes prone to thrombosis. And if a microthrombus forms, it will damage the pregnancy. Although then my gynecologist showed the tests to another hematologist or even a gynecologist. And that other doctor said don't worry, it's okay, the main thing is to control homocysteine during pregnancy.

I don’t know about blood clots, whether this is due to homocysteine or something else.

Wow. and, unfortunately, this is not all for me .. ((I'm still that mutant!

GE4) Plasminogen activator inhibitor gene PAI-1 (5G/4G) - 4G/5G

GE6) Alpha-2 integrin gene GPIa (C807T) - C/T

(GE10) Gene methionine synthase reductase MTRR (A66G) - A/G

(GE8) MTHFR methylenetetrahydrofolate reductase gene (C677 T) - T/T

GE19) Angiotensin converting factor gene ACE(Ins/Del) - D/D

(GE18) G-protein beta 3 gene GNB3 (C825T) - C/T

GE39) N-acetyl transferase gene (NAT2-4,5,6,7,12 alleles) - *5B/*6

(GE36) Mu-glutathione S-transferase gene (GSTM1 gene deletion) - Del/Del

GE38) Gene pi-glutathione S-transferase (GSTP1) - Ile/Val

(GE43) Cytochrome P450 enzyme gene (CYP1A2*1C,*1F) - *1F/*1F

You nailed genetics!

I understand that you need to see Shablis.

Leeches, hyperbaric chamber, oxygen cocktails, physio - these are our best friends.

Chablis. Who is this? In St. Petersburg? I don’t understand at all, is it possible for a mutant like me to bear a child? Too many mutations

I'm such a mutant!!

homozygous for MTHFR, F7, PLAT

heterozygous for MTRR, GPLA, PAI-1, FGB

there were 2 ZB, and in the second saw and angoivitis and chimes and nothing helped

I am currently undergoing hydrotherapy.

I drink angiovit all the time, as soon as I quit immediately homocysteine rises, in May I took a break for a week, and homocysteine immediately rose to 18, on angiovit 8-11.

I often fall into despair, but somewhere in the depths of my soul I still believe that I will be a mother!! and I wish you good luck!!

Tell.

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[email protected]@@@@, I would take hCG before going to the doctor to see the dynamics or vice versa. Re themselves rivers.

Can I trust the result, because I looked only after 40 minutes? Damn, nerves nerves)

i_sh, at work in the morning, call and tell me the temperature, cough. And then some kind of lingering armor.

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Heterozygous mutation state

Help me please.

An analysis for mutations in the Notch 3 gene (Cadasil syndrome) was carried out by direct automatic sequencing

The mutation c.268C T, Arg90Cys was found in the heterozygous state, described in the HGMD mutation database.

Thank you in advance!

Also do not forget to thank the doctors.

geneticist7 22:07

you need to know what caused the examination, who sent it to him and see the conclusion.

The reason for the examination was my condition in which I got to the clinic. I suddenly developed weakness, there was a loss of speech. In Kazan, I went through everything possible analyzes and surveys. Found: Progressive leukoencephalopathy, probably due to isolated cerebral vasculitis, in the form of moderate cognitive impairment, bulbar syndrome, pyramidal insufficiency. Hyperhomocysteinemia. Hypercholesterolemia. The professor recommended to undergo molecular genetic diagnosis of a mutation in the Notch-3 gene.

I already sent the conclusion of the molecular genetic laboratory in my previous letter.

Doctor, help me please! Decipher this conclusion.

geneticist0 20:31

The analysis confirmed the syndrome that the doctor suspected.

Thank you very much for your answer. Now I know that I'm sick. Until the disease completely took over me. Apparently, it will be later. Well, that's my destiny.

I would like to know, however, what a heterozygous mutation is. Obviously, this somehow affects the principle of inheritance of the disease. I have two children, boys. My sister has two girls. She is younger than me, she is 38 years old. I am 44 years old. I inherited the disease from my father. He died at 61. The cause of death was a stroke. His younger brother and older sister are alive and relatively healthy. Their children are also healthy. Really, I'm the only one who got the mutation.

If you answer at least a few of these questions, I will be very grateful to you.

All the best.

geneticist3 10:35

The same probability was for you and your sister. Since she is younger than you, it is not yet known if she inherited.

Your sister and your children can have the same genetic analysis that was done for you. If they want to know now whether they have inherited the mutation or not.

what is a homozygous mutation

Homozygosity and heterozygosity, dominance and recessiveness.

Homozygosity (from the Greek "homo" equal, "zygote" fertilized egg) a diploid organism (or cell) carrying identical alleles in homologous chromosomes.

Gregor Mendel was the first to establish a fact indicating that plants that are similar in appearance can differ sharply in hereditary properties. Individuals that do not split in the next generation are called homozygous. Individuals in whose offspring a splitting of traits is found are called heterozygous.

Homozygosity is a state of the hereditary apparatus of an organism in which homologous chromosomes have the same form of a given gene. The transition of a gene to a homozygous state leads to the manifestation in the structure and function of the organism (phenotype) of recessive alleles, the effect of which, when heterozygous, is suppressed by dominant alleles. The test for homozygosity is the absence of segregation in certain types of crossing. A homozygous organism produces only one type of gamete for this gene.

Heterozygosity is a condition inherent in any hybrid organism in which its homologous chromosomes carry different forms (alleles) of a particular gene or differ in the relative position of the genes. The term "heterozygosity" was first introduced by the English geneticist W. Batson in 1902. Heterozygosity occurs when gametes of different quality in terms of gene or structural composition merge into a heterozygote. Structural heterozygosity occurs when a chromosomal rearrangement of one of the homologous chromosomes occurs, it can be detected in meiosis or mitosis. Heterozygosity is detected by analyzing crosses. Heterozygosity, as a rule, is a consequence of the sexual process, but may result from a mutation. With heterozygosity, the effect of harmful and lethal recessive alleles is suppressed by the presence of the corresponding dominant allele and is manifested only when this gene passes into the homozygous state. Therefore, heterozygosity is widespread in natural populations and is, apparently, one of the causes of heterosis. The masking effect of dominant alleles in heterozygosity is the reason for the preservation and spread of harmful recessive alleles in the population (the so-called heterozygous carriage). Their identification (for example, by testing producers by offspring) is carried out in any breeding and selection work, as well as in the preparation of medical genetic forecasts.

In our own words, we can say that in breeding practice, the homozygous state of the genes is called “correct”. If both alleles that control any characteristic are the same, then the animal is called homozygous, and in breeding by inheritance will pass exactly this characteristic. If one allele is dominant and the other is recessive, then the animal is called heterozygous, and outwardly it will demonstrate a dominant characteristic, and inherit either a dominant characteristic or a recessive one.

Any living organism has a section of DNA (deoxyribonucleic acid) molecules called chromosomes. During reproduction, germ cells carry out copying of hereditary information by their carriers (genes), which make up a section of chromosomes that have the shape of a spiral and are located inside the cells. Genes located in the same loci (strictly defined positions in the chromosome) of homologous chromosomes and determining the development of any trait are called alleles. In a diploid (double, somatic) set, two homologous (identical) chromosomes and, accordingly, two genes just carry the development of these different traits. When one trait predominates over another, it is called dominance, and the genes are dominant. A trait whose expression is suppressed is called recessive. The homozygosity of an allele is the presence in it of two identical genes (carriers of hereditary information): either two dominant or two recessive. The heterozygosity of an allele is the presence of two different genes in it, i.e. one is dominant and the other is recessive. Alleles that in a heterozygote give the same manifestation of any hereditary trait as in a homozygote are called dominant. Alleles that show their effect only in the homozygote, and are invisible in the heterozygote, or are suppressed by the action of another dominant allele, are called recessive.

The principles of homozygosity, heterozygosity and other foundations of genetics were first formulated by the founder of genetics, Abbot Gregor Mendel, in the form of his three laws of inheritance.

Mendel's first law: "Offspring from crossing individuals homozygous for different alleles of the same gene are uniform in phenotype and heterozygous in genotype."

Mendel's second law: "When heterozygous forms are crossed, a regular splitting is observed in the offspring in a ratio of 3: 1 by phenotype and 1: 2: 1 by genotype."

Mendel's third law: “The alleles of each gene are inherited regardless of the body size of the animal.

From the point of view of modern genetics, his hypotheses look like this:

1. Each trait of a given organism is controlled by a pair of alleles. An individual that received the same alleles from both parents is called homozygous and is indicated by two identical letters (for example, AA or aa), and if it receives different ones, then heterozygous (Aa).

2. If the organism contains two different alleles this feature, then one of them (dominant) can manifest itself, completely suppressing the manifestation of the other (recessive). (The principle of dominance or uniformity of the descendants of the first generation). As an example, let's take a monohybrid (only on the basis of color) crossing in cockers. Let's assume that both parents are homozygous for color, so a black dog will have a genotype, which we will designate as AA for example, and a fawn aa. Both individuals will produce only one type of gamete: black only A, and fawn only a. No matter how many puppies are born in such a litter, they will all be black, since the black color is dominant. On the other hand, they will all be carriers of the fawn gene, since their genotype is Aa. For those who have not figured it out too much, we note that the recessive trait (in this case, the fawn color) appears only in the homozygous state!

3. Each sex cell (gamete) receives one of each pair of alleles. (Principle of splitting). If we cross the descendants of the first generation or any two cockers with the Aa genotype, splitting will be observed in the offspring of the second generation: Aa + aa \u003d AA, 2Aa, aa. Thus, the splitting by phenotype will look like 3:1, and by genotype as 1:2:1. That is, when mating two black heterozygous Cockers, we can have 1/4 the probability of producing black homozygous dogs (AA), 2/4 the probability of producing black heterozygotes (Aa) and 1/4 the probability of producing fawn (aa). In life, everything is not so simple. Sometimes two black heterozygous Cockers can produce 6 fawn puppies, or they can all be black. We simply calculate the probability of the appearance of this trait in puppies, and whether it will manifest itself depends on which alleles got into the fertilized eggs.

4. During the formation of gametes, any allele from one pair can get into each of them along with any other from another pair. (Principle of independent distribution). Many traits are inherited independently, for example, if the color of the eyes may depend on the general color of the dog, then it is practically not related to the length of the ears. If we take a dihybrid cross (according to two different traits), then we can see the following ratio: 9: 3: 3: 1

5. Each allele is passed down from generation to generation as a discrete unchanging unit.

b. Each organism inherits one allele (for each trait) from each parent.

If for a specific gene the two alleles carried by an individual are the same, which one will predominate? Since mutation of alleles often results in loss of function (null alleles), an individual carrying only one such allele will also have a "normal" (wild type) allele for the same gene; a single normal copy will often be sufficient to maintain normal function. For an analogy, let's imagine we're building a brick wall, but one of our two regular contractors is on strike. As long as the remaining supplier can supply us with enough bricks, we can continue to build our wall. Geneticists call this phenomenon, when one of the two genes can still provide normal function, dominance. The normal allele is determined to be dominant over the abnormal allele. (In other words, the wrong allele can be said to be recessive to the normal one.)

When one speaks of a genetic abnormality "carried" by an individual or line, it is meant that there is a mutated gene that is recessive. If we do not have sophisticated testing to directly detect this gene, then we will not be able to visually determine the courier (carrier) from an individual with two normal copies (alleles) of the gene. Unfortunately, lacking such testing, the courier will not be detected in time and will inevitably pass on the mutation allele to some of its offspring. Each individual can be similarly "staffed" and carry several of these dark secrets in their genetic baggage (genotype). However, we all have thousands of different genes for many various functions, and as long as these abnormalities are rare, the likelihood that two unrelated individuals carrying the same "abnormality" will meet to reproduce is very low.

Sometimes individuals with a single normal allele may have an "intermediate" phenotype. For example, in the Basenji, which carries one allele for pyruvate kinase deficiency (an enzyme deficiency leading to mild anemia), average duration red life blood cell- 12 days. This is an intermediate type between a normal cycle of 16 days and a cycle of 6.5 days in a dog with two incorrect alleles. Although this is often called incomplete dominance, in this case it would be preferable to say that there is no dominance at all.

Let's take our brick wall analogy a little further. What if a single supply of bricks isn't enough? We'll be left with a wall that's lower (or shorter) than the intended one. Will it matter? It depends on what we want to do with the "wall" and possibly genetic factors. The result may not be the same for the two people who built this wall. (A low wall may keep floods out, but not floods!) If there is a possibility that an individual carrying only one copy of the wrong allele will show it with the wrong phenotype, then that allele should be regarded as dominant. Her refusal to always do so is defined by the term penetrance.

A third possibility is that one of the contractors is supplying us with custom bricks. Not realizing this, we continue to work - as a result, the wall falls. We could say that defective bricks are the dominant factor. Success in understanding several dominant genetic diseases in humans suggests that this is a reasonable analogy. Most dominant mutations affect proteins that are components of large macromolecular complexes. These mutations result in proteins that cannot interact properly with other components, leading to the failure of the entire complex (defective bricks - a fallen wall). Others are found in regulatory sequences adjacent to genes and cause the gene to be transcribed at the wrong time and place.

Dominant mutations can persist in populations if the problems they cause are subtle and not always pronounced, or appear at a mature stage of life after the affected individual has participated in reproduction.

A recessive gene (i.e., a trait determined by it) may not appear in one or many generations until two identical recessive genes from each parent meet (the sudden manifestation of such a trait in offspring should not be confused with a mutation).

Dogs that have only one recessive gene - the determinant of any trait, will not show this trait, since the action of the recessive gene will be masked by the manifestation of the influence of the dominant gene paired with it. Such dogs (carriers of a recessive gene) can be dangerous for the breed if this gene determines the appearance of an undesirable trait, because it will pass it on to their descendants, and they will continue to do so in the breed. If you accidentally or thoughtlessly pair two carriers of such a gene, they will give part of the offspring with undesirable traits.

The presence of a dominant gene is always clearly and outwardly manifested by the corresponding feature. Therefore, dominant genes that carry an undesirable trait are much less dangerous for the breeder than recessive ones, since their presence always appears, even if the dominant gene "works" without a partner (Aa).

But apparently, to complicate matters, not all genes are absolutely dominant or recessive. In other words, some are more dominant than others and vice versa. For example, some factors that determine coat color can be dominant, but still not outwardly manifest unless they are supported by other genes, sometimes even recessive ones.

Matings do not always produce ratios exactly as expected on average, and a large litter or a large number of offspring in multiple litters must be produced to obtain a reliable result from a given mating.

Some external traits may be "dominant" in some breeds and "recessive" in others. Other traits may be due to multiple genes or semi-genes that are not simple dominants or Mendelian recessives.

Diagnostics genetic disorders

Diagnosis of genetic disorders as a doctrine of recognition and designation of genetic diseases consists mainly of two parts

detection pathological signs, that is, phenotypic deviations in individual individuals; proof of the heritability of the detected deviations. The concept of “genetic health assessment” means checking a phenotypically normal individual to identify unfavorable recessive alleles (heterozygosity test). Along with genetic methods, methods are also used that exclude the influence of the environment. Routine research methods: grading, laboratory diagnostics, methods pathological anatomy, histology and pathophysiology. Special Methods of great importance - cytogenetic and immunogenetic methods. The cell culture method has contributed to significant advances in the diagnosis and genetic analysis of hereditary diseases. In a short time, this method made it possible to study about 20 genetic defects found in humans (Rerabek and Rerabek, 1960; New, 1956; Rapoport, 1969) with its help it is possible in many cases to differentiate homozygotes from heterozygotes with a recessive type of inheritance

Immunogenetic methods are used to study blood groups, blood and milk serum proteins, seminal fluid proteins, hemoglobin types, etc. Discovery a large number protein loci with multiple alleles led to a "renaissance" in Mendelian genetics. Protein loci are used:

to establish the genotype of individual animals

when examining some specific defects (immunoparesis)

to study linkage (genes markers)

for genetic incompatibility analysis

to detect mosaicism and chimerism

The presence of a defect from the moment of birth, defects that appear in certain lines and nurseries, the presence of a common ancestor in each abnormal case - does not mean the heredity of this condition and the genetic nature. When a pathology is detected, it is necessary to obtain evidence of its genetic conditionality and determine the type of inheritance. Statistical processing of the material is also necessary. Genetic-statistical analysis is subjected to two groups of data:

Population data - frequency of congenital anomalies in the cumulative population, frequency of congenital anomalies in the subpopulation

Family data - proof of genetic conditioning and determination of the type of inheritance, inbreeding coefficients and the degree of concentration of ancestors.

When studying genetic conditioning and type of inheritance, the observed numerical ratios of normal and defective phenotypes in the offspring of a group of parents of the same (theoretically) genotype are compared with splitting ratios calculated on the basis of binomial probabilities according to Mendel's laws. To obtain statistical material, it is necessary to calculate the frequency of affected and healthy individuals among the blood relatives of the proband over several generations, determine the numerical ratio by combining individual data, combine data on small families with correspondingly identical parental genotypes. Also important is information about the size of the litter and the sex of the puppies (to assess the possibility of sex-linked or sex-limited heredity).

In this case, it is necessary to collect data for the selection:

Complex selection - a random sample of parents (used when checking a dominant trait)

Purposeful selection - all dogs with a "bad" sign in the population after a thorough examination of it

Individual selection - the probability of an anomaly is so low that it occurs in one puppy from a litter

Multiple selection - intermediate between purposeful and individual, when there is more than one affected puppy in the litter, but not all of them are probands.

All methods, except for the first one, exclude the mating of dogs with the Nn genotype, which do not give anomalies in the litters. Exist various ways data correction: N.T.J. Bailey (79), L.L. Kavaii-Sforza and V.F. Bodme and K. Stehr.

Genetic characterization of a population begins with an estimate of the prevalence of the disease or trait under study. These data are used to determine the frequencies of genes and corresponding genotypes in the population. The population method makes it possible to study the distribution of individual genes or chromosomal abnormalities in populations. To analyze the genetic structure of a population, it is necessary to examine a large group of individuals, which must be representative, allowing one to judge the population as a whole. This method is informative in the study of various forms of hereditary pathology. The main method in determining the type of hereditary anomalies is the analysis of pedigrees within the related groups of individuals in which cases of the studied disease were recorded according to the following algorithm:

Determination of the origin of anomalous animals by breeding cards;

Drawing up pedigrees for anomalous individuals in order to search for common ancestors;

Analysis of the type of inheritance of the anomaly;

Carrying out genetic and statistical calculations on the degree of randomness of the appearance of an anomaly and the frequency of occurrence in the population.

The genealogical method for analyzing pedigrees occupies a leading position in genetic studies of slowly breeding animals and humans. By studying the phenotypes of several generations of relatives, it is possible to establish the nature of the inheritance of the trait and the genotypes of individual family members, to determine the likelihood of manifestation and the degree of risk for offspring for a particular disease.

When determining a hereditary disease, attention is paid to typical signs genetic predisposition. Pathology occurs more often in a group of related animals than in the whole population. This helps to distinguish a congenital disease from a breed predisposition. However, analysis of the pedigree shows that there are familial cases of the disease, which suggests the presence of a particular gene or group of genes responsible for it. Secondly, a hereditary defect often affects the same anatomical region in a group of related animals. Thirdly, with inbreeding, there are more cases of the disease. Fourth, hereditary diseases often present early and often have a constant age of onset.

Genetic diseases usually affect several animals in a litter, unlike intoxication and infectious diseases that affect the entire litter. congenital diseases very diverse, from relatively benign to invariably lethal. Diagnosis is usually based on history taking, clinical signs, history of disease in related animals, results of test crosses, and certain diagnostic tests.

A significant number of monogenic diseases are inherited in a recessive manner. This means that with the autosomal localization of the corresponding gene, only homozygous mutation carriers are affected. Mutations are most often recessive and appear only in the homozygous state. Heterozygotes are clinically healthy, but are equally likely to pass on the mutant or normal version of the gene to their children. Thus, for a long time, a latent mutation can be passed from generation to generation. With an autosomal recessive type of inheritance in the pedigrees of seriously ill patients who either do not live to see reproductive age, or have a sharply reduced potency for reproduction, it is rarely possible to identify sick relatives, especially in the ascending line. The exception is families with increased level inbreeding.

Dogs that have only one recessive gene - the determinant of any trait, will not show this trait, since the action of the recessive gene will be masked by the manifestation of the influence of the dominant gene paired with it. Such dogs (carriers of a recessive gene) can be dangerous for the breed if this gene determines the appearance of an undesirable trait, because it will pass it on to their descendants. If you accidentally or deliberately pair two carriers of such a gene, they will give part of the offspring with undesirable traits.

The expected ratio of splitting offspring according to one trait or another is approximately justified with a litter of at least 16 puppies. For a litter of normal size puppies, one can only talk about a greater or lesser probability of a trait determined by a recessive gene for the offspring of a certain pair of sires with a known genotype.

The selection of recessive anomalies can be carried out in two ways. The first of these is to exclude from breeding dogs with manifestations of anomalies, i.e., homozygotes. The occurrence of an anomaly with such selection in the first generations decreases sharply, and then more slowly, remaining at a relatively low level. The reason for the incomplete elimination of some anomalies even during a long and stubborn selection is, firstly, a much slower reduction in carriers of recessive genes than homozygotes. Secondly, in the fact that with mutations that slightly deviate from the norm, breeders do not always discard abnormal dogs and carriers.

With an autosomal recessive type of inheritance:

A trait can be passed down through generations even with a sufficient number of offspring

The trait may appear in children in the (apparent) absence of it in the parents. Found then in 25% of cases in children

The trait is inherited by all children if both parents are sick

A sign in 50% develops in children if one of the parents is sick

Male and female offspring inherit this trait equally.

Thus, the absolutely complete elimination of the anomaly is possible in principle, provided that all carriers are identified. The scheme of such detection: heterozygotes for recessive mutations can in some cases be detected laboratory methods research. However, for the genetic identification of heterozygous carriers, it is necessary to conduct analyzing crosses - matings suspected as a carrier dog with a homozygous abnormal (if the anomaly slightly affects the body) or with a previously established carrier. If, among others, abnormal puppies are born as a result of such crosses, the tested sire is clearly identified as a carrier. However, if such puppies were not identified, then an unambiguous conclusion cannot be made on a limited sample of the obtained puppies. The probability that such a sire is a carrier decreases with the expansion of the sample - an increase in the number of normal puppies born from matings with him.

At the Department of the Veterinary Academy of St. Petersburg, an analysis of the structure of the genetic load in dogs was carried out and it was found that the largest proportion - 46.7% are anomalies inherited according to a monogenic autosomal recessive type; anomalies with complete dominance amounted to 14.5%; 2.7% of anomalies appeared as non-full-dominant signs; 6.5% of anomalies are inherited as sex-linked, 11.3% of hereditary traits with a polygenic type of inheritance and 18%3% of the entire spectrum of hereditary anomalies, the type of inheritance has not been established. Total number anomalies and diseases with a hereditary basis in dogs amounted to 186 items.

Along with traditional methods The use of phenotypic markers of mutations is topical for selection and genetic prophylaxis.

Genetic disease monitoring is a direct method for assessing hereditary diseases in the offspring of unaffected parents. "Sentinel" phenotypes can be: cleft palate, cleft lip, inguinal and umbilical hernias, dropsy of newborns, convulsions in newborn puppies. In monogenic fixed diseases, it is possible to identify the actual carrier through the marker gene associated with it.

The existing breed diversity of dogs presents a unique opportunity to study the genetic control of numerous morphological traits, the various combinations of which determine breed standards. This situation can be illustrated by two of the existing breeds domestic dog, contrastingly different from each other at least in such morphological features like height and weight. This is the English Mastiff breed, on the one hand, whose representatives have a height at the withers of up to 80 cm and a body weight of more than 100 kg, and the Chi Hua Hua breed, 30 cm and 2.5 kg.

The process of domestication involves the selection of animals for their most outstanding traits, from a human point of view. Over time, when the dog began to be kept as a companion and for its aesthetic appearance, the direction of selection changed to obtaining breeds poorly adapted to survival in nature, but well adapted to the human environment. There is an opinion that "mongrels" are healthier than purebred dogs. Indeed, hereditary diseases are probably more common in domestic animals than in wild ones.

“One of the most important goals is to develop methods for combining the tasks of improving animals according to breeding traits and maintaining their fitness at the required level - as opposed to one-sided selection that is dangerous for the biological well-being of domesticated organisms for the maximum (sometimes exaggerated, excessive) development of specific breed traits” - (Lerner, 1958).

The effectiveness of selection, in our opinion, should consist in diagnosing anomalies in affected animals and identifying carriers with defective heredity, but with a normal phenotype. Treatment of affected animals in order to correct their phenotypes can be considered not only as an measure to improve the aesthetic appearance of animals (oligodontia), but also to prevent cancer (cryptorchidism), maintain biological, full-fledged activity (hip dysplasia) and stabilize health in general. In this regard, selection against anomalies is necessary when joint activities cynology and veterinary medicine.

Ability to test DNA for various diseases Dogs are a very new thing in cynology, knowing this can alert breeders to which genetic diseases to look out for when matching sire pairs. Good genetic health is very important because it determines biologically full life dogs. Dr. Padgett's book, Hereditary Disease Control in Dogs, shows how to read a genetic lineage for any abnormality. Genetic pedigrees will show whether the disease is sex-linked, inherited through a simple dominant gene, or through a recessive one, or if the disease is polygenic in origin. Unintentional genetic errors will occur from time to time no matter how careful the breeder is. Using genetic lineages as a vehicle for knowledge sharing, it is possible to dilute "bad" genes to the point of stopping them from appearing until a DNA marker is found to test for their transmission. Since the breeding process involves the improvement of the population in the next generation, it is not the phenotypic characteristics of the direct elements of the breeding strategy (individuals or pairs of crossed individuals) that are taken into account, but the phenotypic characteristics of their descendants. It is in connection with this circumstance that the need arises to describe the inheritance of a trait for selection problems. A pair of interbreeding individuals differ from the rest of the same individuals in their origin and phenotypic characteristics sign, both of themselves and of their relatives. Based on these data, if there is a ready description of inheritance, it is possible to obtain the expected characteristics of the offspring and, consequently, estimates of the breeding values of each of the elements of the breeding strategy. In any action taken against any genetic anomaly, the first step is to determine the relative importance of the "bad" trait compared to other traits. If the undesirable trait has a high heritability and causes serious damage to the dog, you should proceed differently than if the trait is rare or of minor importance. A dog of excellent breed type that transmits a faulty color remains a much more valuable sire than a mediocre one with the correct color.

There may be mutations in different places, by the way.

When a mutant MTHFR gene is detected in a heterozygous state*, there are no good reasons for fear. As a preventive measure for hypercoagulable conditions, it is recommended to take folic acid 0.4 mg / day in two doses daily during pregnancy, eat well and examine the hemostasiogram once every three months (or according to indications).

The most common enzyme defect that is associated with a moderate increase in HC (homocysteine) levels is a mutation in the gene encoding MTHFR. MTHFR catalyzes the conversion of folic acid to its active form. To date, 9 mutations of the MTHFR gene located at the 1p36.3 locus have been described. The most common of these is the C677T substitution (in the MTHFR protein - the substitution of alanine for valine), which is manifested by thermolability and a decrease in the activity of the MTHFR enzyme. It has been observed that an increase in the content of folate in food can prevent an increase in the concentration of HC in plasma.

An increase in the level of homocysteine in the blood plasma directly correlates with the inhibition of thrombomodulin synthesis, a decrease in the activity of AT-III and endogenous heparin, and also with the activation of the production of thromboxane A2. In the future, such changes cause microthrombosis and microcirculation disorders, which, in turn, plays a significant role in the pathology of the spiral arteries and the development of obstetric complications associated with changes in the uteroplacental circulation. link

The reason for the elevated blood homocysteine level: C677T variant in the MTHFR gene is a mutation in the gene for the enzyme methylenetetrahydrofolate reductase.

The replacement of cytosine with thymine at position 677 leads to a decrease in the functional activity of the enzyme to 35% of the average value.

Polymorphism data:

*frequency of occurrence of homozygotes in the population - 10-12%

* frequency of occurrence of heterozygotes in the population - 40%

Carriers of the T variant are deficient in folic acid during pregnancy, leading to neural tube defects in the fetus.

Smoking exacerbates the effects of the 677T variant.

The appointment of folic acid can significantly reduce the risk of the consequences of this variant of the polymorphism.

In general, who will be taken where ... It is impossible to say for sure. It also depends on the father - what is in his genome.

Try asking your question in more detail here - link

Everything is in the power of God. Here the statistics are powerless.

Heterozygous mutation state

Help me please.

An analysis for mutations in the Notch 3 gene (Cadasil syndrome) was carried out by direct automatic sequencing

The mutation c.268C T, Arg90Cys was found in the heterozygous state, described in the HGMD mutation database.

Thank you in advance!

Also do not forget to thank the doctors.

geneticist7 22:07

you need to know what caused the examination, who sent it to him and see the conclusion.

The reason for the examination was my condition in which I got to the clinic. I suddenly developed weakness, there was a loss of speech. In Kazan, I went through all possible tests and examinations. Found: Progressive leukoencephalopathy, probably due to isolated cerebral vasculitis, in the form of moderate cognitive impairment, bulbar syndrome, pyramidal insufficiency. Hyperhomocysteinemia. Hypercholesterolemia. The professor recommended to undergo molecular genetic diagnosis of a mutation in the Notch-3 gene.

I already sent the conclusion of the molecular genetic laboratory in my previous letter.

Doctor, help me please! Decipher this conclusion.

The analysis confirmed the syndrome that the doctor suspected.

Thank you very much for your answer. Now I know that I'm sick. Until the disease completely took over me. Apparently, it will be later. Well, that's my destiny.

If you answer at least a few of these questions, I will be very grateful to you.

All the best.

geneticist3 10:35

The same probability was for you and your sister. Since she is younger than you, it is not yet known if she inherited.

Your sister and your children can have the same genetic analysis that was done for you. If they want to know now whether they have inherited the mutation or not.

Heterozygous mutation what does it mean

Homozygosity and heterozygosity, dominance and recessiveness.

Homozygosity (from the Greek "homo" equal, "zygote" fertilized egg) a diploid organism (or cell) carrying identical alleles in homologous chromosomes.

The principles of homozygosity, heterozygosity and other foundations of genetics were first formulated by the founder of genetics, Abbot Gregor Mendel, in the form of his three laws of inheritance.

Mendel's first law: "Offspring from crossing individuals homozygous for different alleles of the same gene are uniform in phenotype and heterozygous in genotype."

Mendel's second law: "When heterozygous forms are crossed, a regular splitting is observed in the offspring in a ratio of 3: 1 by phenotype and 1: 2: 1 by genotype."

Mendel's third law: “The alleles of each gene are inherited regardless of the body size of the animal.

From the point of view of modern genetics, his hypotheses look like this:

2. If an organism contains two different alleles of a given trait, then one of them (dominant) can manifest itself, completely suppressing the manifestation of the other (recessive). (The principle of dominance or uniformity of the descendants of the first generation). As an example, let's take a monohybrid (only on the basis of color) crossing in cockers. Let's assume that both parents are homozygous for color, so a black dog will have a genotype, which we will designate as AA for example, and a fawn aa. Both individuals will produce only one type of gamete: black only A, and fawn only a. No matter how many puppies are born in such a litter, they will all be black, since the black color is dominant. On the other hand, they will all be carriers of the fawn gene, since their genotype is Aa. For those who have not figured it out too much, we note that the recessive trait (in this case, the fawn color) appears only in the homozygous state!

5. Each allele is passed down from generation to generation as a discrete unchanging unit.

b. Each organism inherits one allele (for each trait) from each parent.

When one speaks of a genetic abnormality "carried" by an individual or line, it is meant that there is a mutated gene that is recessive. If we do not have sophisticated testing to directly detect this gene, then we will not be able to visually determine the courier (carrier) from an individual with two normal copies (alleles) of the gene. Unfortunately, lacking such testing, the courier will not be detected in time and will inevitably pass on the mutation allele to some of its offspring. Each individual can be similarly "staffed" and carry several of these dark secrets in their genetic baggage (genotype). However, we all have thousands of different genes for many different functions, and as long as these abnormalities are rare, the likelihood that two unrelated individuals carrying the same "abnormality" will meet to reproduce is very low.

Sometimes individuals with a single normal allele may have an "intermediate" phenotype. For example, in the Basenji, which carries one allele for pyruvate kinase deficiency (an enzyme deficiency leading to mild anemia), the average lifespan of a red blood cell is 12 days. This is an intermediate type between a normal cycle of 16 days and a cycle of 6.5 days in a dog with two incorrect alleles. Although this is often called incomplete dominance, in this case it would be preferable to say that there is no dominance at all.

A recessive gene (i.e., a trait determined by it) may not appear in one or many generations until two identical recessive genes from each parent meet (the sudden manifestation of such a trait in offspring should not be confused with a mutation).

Some external traits may be "dominant" in some breeds and "recessive" in others. Other traits may be due to multiple genes or semi-genes that are not simple dominants or Mendelian recessives.

Diagnosis of genetic disorders

Diagnosis of genetic disorders as a doctrine of recognition and designation of genetic diseases consists mainly of two parts

identification of pathological signs, that is, phenotypic abnormalities in individual individuals; proof of the heritability of the detected deviations. The concept of “genetic health assessment” means checking a phenotypically normal individual to identify unfavorable recessive alleles (heterozygosity test). Along with genetic methods, methods are also used that exclude the influence of the environment. Routine research methods: evaluation, laboratory diagnostics, methods of pathological anatomy, histology and pathophysiology. Special methods of great importance are cytogenetic and immunogenetic methods. The cell culture method has contributed to significant advances in the diagnosis and genetic analysis of hereditary diseases. In a short time, this method made it possible to study about 20 genetic defects found in humans (Rerabek and Rerabek, 1960; New, 1956; Rapoport, 1969) with its help it is possible in many cases to differentiate homozygotes from heterozygotes with a recessive type of inheritance

Immunogenetic methods are used to study blood groups, blood serum and milk proteins, seminal fluid proteins, types of hemoglobin, etc. The discovery of a large number of protein loci with multiple alleles led to a "renaissance" in Mendelian genetics. Protein loci are used:

to establish the genotype of individual animals

when examining some specific defects (immunoparesis)

to study linkage (genes markers)

for genetic incompatibility analysis

to detect mosaicism and chimerism

Population data - frequency of congenital anomalies in the cumulative population, frequency of congenital anomalies in the subpopulation

Family data - proof of genetic conditioning and determination of the type of inheritance, inbreeding coefficients and the degree of concentration of ancestors.

In this case, it is necessary to collect data for the selection:

Complex selection - a random sample of parents (used when checking a dominant trait)

Purposeful selection - all dogs with a "bad" sign in the population after a thorough examination of it

Individual selection - the probability of an anomaly is so low that it occurs in one puppy from a litter

Multiple selection - intermediate between purposeful and individual, when there is more than one affected puppy in the litter, but not all of them are probands.

All methods, except for the first one, exclude the mating of dogs with the Nn genotype, which do not give anomalies in the litters. There are various ways to correct data: N.T.J. Bailey (79), L.L. Kavaii-Sforza and V.F. Bodme and K. Stehr.

Determination of the origin of anomalous animals by breeding cards;

Drawing up pedigrees for anomalous individuals in order to search for common ancestors;

Analysis of the type of inheritance of the anomaly;

Carrying out genetic and statistical calculations on the degree of randomness of the appearance of an anomaly and the frequency of occurrence in the population.

When determining a hereditary disease, attention is paid to the typical signs of a genetic predisposition. Pathology occurs more often in a group of related animals than in the whole population. This helps to distinguish a congenital disease from a breed predisposition. However, analysis of the pedigree shows that there are familial cases of the disease, which suggests the presence of a particular gene or group of genes responsible for it. Secondly, a hereditary defect often affects the same anatomical region in a group of related animals. Thirdly, with inbreeding, there are more cases of the disease. Fourth, hereditary diseases often present early and often have a constant age of onset.

Genetic diseases usually affect a few animals in a litter, as opposed to intoxication and infectious diseases that affect the entire litter. Congenital diseases are very diverse, from relatively benign to invariably fatal. Diagnosis is usually based on history taking, clinical signs, history of illness in related animals, results of test crosses, and certain diagnostic tests.

A significant number of monogenic diseases are inherited in a recessive manner. This means that with the autosomal localization of the corresponding gene, only homozygous mutation carriers are affected. Mutations are most often recessive and appear only in the homozygous state. Heterozygotes are clinically healthy, but are equally likely to pass on the mutant or normal version of the gene to their children. Thus, for a long time, a latent mutation can be passed from generation to generation. With an autosomal recessive type of inheritance in the pedigrees of seriously ill patients who either do not live to reproductive age, or have a sharply reduced potency for reproduction, it is rarely possible to identify sick relatives, especially in the ascending line. The exception is families with a high level of inbreeding.

Dogs that have only one recessive gene - the determinant of any trait, will not show this trait, since the action of the recessive gene will be masked by the manifestation of the influence of the dominant gene paired with it. Such dogs (carriers of a recessive gene) can be dangerous for the breed if this gene determines the appearance of an undesirable trait, because it will pass it on to their descendants. If you accidentally or deliberately pair two carriers of such a gene, they will give part of the offspring with undesirable traits.

With an autosomal recessive type of inheritance:

A trait can be passed down through generations even with a sufficient number of offspring

The trait may appear in children in the (apparent) absence of it in the parents. Found then in 25% of cases in children

The trait is inherited by all children if both parents are sick

A sign in 50% develops in children if one of the parents is sick

Male and female offspring inherit this trait equally.

Thus, the absolutely complete elimination of the anomaly is possible in principle, provided that all carriers are identified. The scheme of such detection: heterozygotes for recessive mutations can in some cases be detected by laboratory research methods. However, for the genetic identification of heterozygous carriers, it is necessary to conduct analyzing crosses - matings suspected as a carrier dog with a homozygous abnormal (if the anomaly slightly affects the body) or with a previously established carrier. If, among others, abnormal puppies are born as a result of such crosses, the tested sire is clearly identified as a carrier. However, if such puppies were not identified, then an unambiguous conclusion cannot be made on a limited sample of the obtained puppies. The probability that such a sire is a carrier decreases with the expansion of the sample - an increase in the number of normal puppies born from matings with him.

At the Department of the Veterinary Academy of St. Petersburg, an analysis of the structure of the genetic load in dogs was carried out and it was found that the largest proportion - 46.7% are anomalies inherited according to a monogenic autosomal recessive type; anomalies with complete dominance amounted to 14.5%; 2.7% of anomalies appeared as non-full-dominant signs; 6.5% of anomalies are inherited as sex-linked, 11.3% of hereditary traits with a polygenic type of inheritance and 18%3% of the entire spectrum of hereditary anomalies, the type of inheritance has not been established. The total number of anomalies and diseases with a hereditary basis in dogs was 186 items.

Along with the traditional methods of selection and genetic prevention, the use of phenotypic markers of mutations is relevant.

The existing breed diversity of dogs presents a unique opportunity to study the genetic control of numerous morphological traits, the various combinations of which determine breed standards. An illustration of this situation can serve as two of the currently existing breeds of domestic dogs, contrastingly different from each other at least in such morphological features as height and weight. This is the English Mastiff breed, on the one hand, whose representatives have a height at the withers of up to 80 cm and a body weight of more than 100 kg, and the Chi Hua Hua breed, 30 cm and 2.5 kg.

The effectiveness of selection, in our opinion, should consist in diagnosing anomalies in affected animals and identifying carriers with defective heredity, but with a normal phenotype. Treatment of affected animals in order to correct their phenotypes can be considered not only as an measure to improve the aesthetic appearance of animals (oligodontia), but also to prevent cancer (cryptorchidism), maintain biological, full-fledged activity (hip dysplasia) and stabilize health in general. In this regard, selection against anomalies is necessary in the joint activities of cynology and veterinary medicine.

The ability to test DNA for various dog diseases is a very new thing in canine science, knowing this can alert breeders to which genetic diseases to look out for when matching sire pairs. Good genetic health is very important because it determines a dog's biologically fulfilling life. Dr. Padgett's book, Hereditary Disease Control in Dogs, shows how to read a genetic lineage for any abnormality. Genetic pedigrees will show whether the disease is sex-linked, inherited through a simple dominant gene, or through a recessive one, or if the disease is polygenic in origin. Unintentional genetic errors will occur from time to time no matter how careful the breeder is. Using genetic lineages as a vehicle for knowledge sharing, it is possible to dilute "bad" genes to the point of stopping them from appearing until a DNA marker is found to test for their transmission. Since the breeding process involves the improvement of the population in the next generation, it is not the phenotypic characteristics of the direct elements of the breeding strategy (individuals or pairs of crossed individuals) that are taken into account, but the phenotypic characteristics of their descendants. It is in connection with this circumstance that the need arises to describe the inheritance of a trait for selection problems. A pair of interbreeding individuals differ from the rest of the same individuals in their origin and phenotypic characteristics of the trait, both themselves and their relatives. Based on these data, if there is a ready description of inheritance, it is possible to obtain the expected characteristics of the offspring and, consequently, estimates of the breeding values of each of the elements of the breeding strategy. In any action taken against any genetic anomaly, the first step is to determine the relative importance of the "bad" trait compared to other traits. If the undesirable trait has a high heritability and causes serious damage to the dog, you should proceed differently than if the trait is rare or of minor importance. A dog of excellent breed type that transmits a faulty color remains a much more valuable sire than a mediocre one with the correct color.