Genes of dominant signs of cataract. Cataract is a dominant gene. Types of inheritance of traits in humans

A gene is a specific sequence of deoxyribonucleic acid nucleotides that encodes genetic information (information regarding the primary structure of protein molecules). The DNA molecule is double stranded. Each of the chains carries a specific sequence of nucleotides. The primary structure of a protein, which is the number and sequence of amino acids, plays a decisive role in hereditary traits. In order for the encoded information to be read correctly and regularly, a gene must have an initiation codon, a termination codon, and sense codons that directly encode the necessary amino acid sequence. Codons are three consecutive nucleotides that code for a specific amino acid. The codons UAA, UAG, UGA are empty and do not code for any of the existing amino acids; when they are read, the replication process stops. The remaining codons (in the amount of 61 pieces) code for amino acids.

Allocate . A dominant gene is a sequence of nucleotides that ensures the manifestation of a particular trait (regardless of which type of gene is in the same pair (meaning a recessive or dominant gene)). A recessive gene is a nucleotide sequence in which the manifestation of a trait in the phenotype is possible only if the same recessive gene is present in a pair.

Such information carries only genetic data that can be passed down from generation to generation. However, the manifestation of one or another trait depends only on the variants of the combination of genes. If there is a recessive and dominant gene in the pair, then the property encoded by the dominant one will phenotypically manifest itself. And only in the case of a combination of two recessive genes, their information appears. That is, the dominant gene suppresses the recessive one.

Where do genes come from?

The information that our genes carry comes from our ancestors. These include not only parents, but also grandparents and other blood relatives. Individual set A gene is formed by the fusion of a spermatozoon and an egg, or rather, by the fusion of X and Y chromosomes, or two X chromosomes. Both the X and Y chromosomes can bring information from the father, while only the X chromosome can bring information from the mother.

It is known that the X chromosome contains more information, so women are more resistant to diseases of various nature than the male population. In theory, the number of newborn boys and girls should be equal, but in practice boys are born. As a result, based on these two facts, there is a balancing of the two sexes. The higher birth rate of the male population is compensated by the greater resistance to various kinds of influences that is characteristic of women.

Genetic Engineering

At the moment, an intensive study of genetic material is underway. Methods for isolation, cloning and hybridization of individual genes have been developed. This is the most important step in creating the future. Such close attention to this issue provoked many hypotheses and hopes. After all, a detailed study can allow humanity to plan the properties and characteristics of the future generation, avoid many diseases and grow organs and their systems for transplantation.

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

All the characteristic features of our body are manifested under the action of genes. Sometimes only one gene is responsible for this, but most often it happens that several units of heredity at once 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 the color of skin, hair, eyes, the degree of mental development depends on the activity of many genes at once. This inheritance is not exactly subject to the laws of Mendel, but goes far beyond it.

The study of human genetics is not only interesting, but also important in terms of understanding the inheritance of various hereditary diseases. Now it is becoming quite relevant to turn young couples to genetic consultations so that, after analyzing the pedigree of each spouse, one could 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, then you can predict the likelihood of its manifestation in offspring. All signs in the body can be divided into dominant and recessive. The interaction between them is not so simple, and sometimes it is not enough to know which one belongs to which category.

Now in the scientific world there are the following types of inheritance in humans:

These types of inheritance, in turn, are also subdivided into some varieties.

Monogenic inheritance is based on Mendel's first and second laws. The 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 kind of inheritance of traits in humans obeys Mendeleev's laws. Given 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.

Hollandic inheritance.

Each type of inheritance has its own characteristics and characteristics.

Signs of autosomal dominant inheritance

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

The type of inheritance is autosomal dominant has the following features:

The diseased trait manifests itself 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 equally transmitted from men and women.

The stronger the effect on reproductive functions, the greater the likelihood of various mutations.

If both parents are sick, then the child, being born homozygous for this trait, is more seriously ill compared to the heterozygote.

All these signs are realized only under the condition of complete dominance. In this case, only the presence of one dominant gene will be sufficient for the manifestation of a trait. An autosomal dominant inheritance pattern can be observed in humans with the inheritance of freckles, curly hair, brown eyes and many others.

Autosomal dominant traits

Most of the individuals 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 for pathological signs, but some quite normal ones are inherited in this way.

Among normal signs with this type of inheritance can be noted:

Curly hair.
Dark eyes.
Straight nose.
Hump on 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 type of inheritance, the following are best known:

Multi-toedness, can be both on the hands and on the feet.
Fusion of the tissues of the phalanges of the fingers.
Brachydactyly.
Myopia.

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

Autosomal recessive inheritance pattern

A sign with this type of inheritance can appear only in the case of the formation of a homozygous for this pathology. Such diseases are more severe because both alleles of the same gene are defective.

The likelihood of such symptoms increases with closely related marriages, so in many countries it is forbidden 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 the pathological gene, then the child will be sick.
The gender of the unborn child does not play any role in inheritance.
In one married couple, the risk of having a second child with the same pathology is 25%.
If you look at the pedigree, then there is 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 second is a carrier of such a gene, then the probability of having a sick child is 50%

Many diseases related to metabolism are inherited by this type.

Type of inheritance linked to the X chromosome

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

Both sexes can be affected, but women are 2 times more likely.
If the 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 reward children of both sexes with such a disease.
The disease is more severe in men, because they do not have a second X chromosome.

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

A sick child can also be born to phenotypically healthy parents.
Most often, men get sick, and women are carriers of the diseased gene.
If the father is sick, then there is no need to worry about the health of the sons, they cannot get a defective gene from him.
The probability of having a sick child in a carrier woman is 25% if we are talking about boys, it rises to 50%.

This is how diseases such as hemophilia, color blindness, muscular dystrophy, Kallmann's 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 such diseases.
Individuals of both sexes are equally affected.
Phenotypic demorphism is clearly manifested.
If a mutation of a dominant gene occurs in gametes, then it will most likely manifest itself in the first generation. It has already been proven that men with age increase the risk of obtaining such mutations, which means that they can reward their children with 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 and 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 these diseases can manifest themselves to varying degrees in different patients.

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

The following symptoms of this syndrome can be listed:

Skinny physique.
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 the muscles and bones.
Early development of osteoarthritis.
Rachiocampsis.
Too flexible joints.
Possibly a speech impediment.
Visual disturbances.

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

It can be noted that some symptoms of the disease do not appear in childhood, but become apparent somewhat later.

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

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

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

Erratic movements combined with reduced tone.
antisocial behavior.
Apathy and irritability.
Manifestation of the schizophrenic type.
Mood swings.

Treatment is directed only at eliminating or reducing symptoms. Tranquilizers, neuroleptics are used. No treatment can stop the development of the disease, therefore, approximately 15-17 years after the onset of the first symptoms, death occurs.

Polygenic inheritance

Many traits and diseases are inherited in an autosomal dominant manner. What it is is already clear, but in most cases it is not so simple. Very often, not one, but several genes are inherited at the same time. They appear in specific environmental conditions.

A distinctive feature of this inheritance is the ability to enhance the individual action of each gene. The main features of this 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 such a trait, the higher the risk of this disease in future descendants.

All considered types of inheritance are related to classic options, 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 a visit to a genetic consultation. A competent specialist will help you understand your pedigree and assess the risk of having a child with abnormalities.

Large English-Russian and Russian-English dictionary. 2001 .

See what a "recessive gene" is in other dictionaries:

recessive gene- (Recessive) genetic information that can be suppressed by the influence of a dominant gene and does not appear in the phenotype. A recessive gene is capable of providing the manifestation of the trait it defines only if it is paired with ... Wikipedia

recessive gene- * recessive gene * recessive gene in a diploid organism, a gene that is phenotypically manifested in the homozygous state (), and in heterozygotes (see) is masked by the dominant allele. The dominant gene determines the formation of a functional product ... Genetics. encyclopedic Dictionary

recessive gene- Genetic information relating to a particular property of an organism. can be suppressed by the influence of dominant genea and, therefore, does not appear in the phenotype. It is believed that the properties represented by recessive genes are manifested in ... ... Great psychological encyclopedia

RECESSIVE GENE- RECESSIVE GENE, in genetics, a type of GENE (ALLELE), which does not appear when crossed with a DOMINANT allele. Despite the fact that it is part of the GENOTYPE (genetic structure) of a HETEROZYGOTE (an organism containing both dominant and ... ... Scientific and technical encyclopedic dictionary

recessive gene- Gene suppressed by dominant Biotechnology topics EN recessive gene ... Technical Translator's Guide

recessive gene- recesyvusis genas statusas T sritis augalininkyste apibreztis Vienas genas is aleliniu genu poros, kurio veikima heterozigotineje padetyje nustelbia kitas genas. atitikmenys: engl. recessive gene rus. recessive rysiai gene: sinonimas - ... ... Zemes ukio augalu selekcijos ir seklininkystes terminu zodynas

recessive trait- A recessive trait is a trait that does not appear in heterozygous individuals due to the suppression of the manifestation of the recessive allele. Recessive traits are traits whose manifestation in hybrids of the first generation is suppressed under the condition ... ... Wikipedia

crossover modifier gene- * crossing over modifier gene gene that changes the frequency of recombination (both in "its" linkage group and in other groups) and in some cases does not have other phenotypic manifestations. Mutant gene * mutant gene * mutant ... Genetics. encyclopedic Dictionary

recessive gene- a gene capable of providing the manifestation of the trait it defines only when it is not paired with the corresponding dominant gene. Dictionary of practical psychologist. Moscow: AST, Harvest. S. Yu. Golovin. 1998 ... Big Psychological Encyclopedia

recessive allele- The allele in which the recessive gene is located Biotechnology topics EN recessive allele ... Technical translator's guide

recessive p allele- Recessive, r. allele * retsesіўny, r. allele * recessive or recessive allele . Recessive gene ... Genetics. encyclopedic Dictionary

Polydactyly and cataract are autosomal dominant

signs. Allelic genes responsible for the development of five-fingeredness and normal

vision, are located in one pair of homologous chromosomes and are closely linked to each other

friend. A man who suffers only from polydactyly and a woman entered into marriage,

suffering only from cataracts. Their son is healthy.

suffering only from polydactyly?

r Aavv (polydactyly) ? aabb (cataract)

F1 AaBv (polydactyly, cataract), Aavv (polydactyly) , aaBv (cataract), aavb (healthy)

Dominant and recessive genes;

There are two types of alleles (gene variants)- dominant and recessive.

Dominant a gene is called, the functional activity of which does not depend on the presence in the body of another gene of this trait. The dominant gene is thus dominant, it appears already in the first generation.

recessive called a gene that provides the development of a trait only in the absence of other variants of this gene in the body. The recessive gene may appear in the second and subsequent generations. For the manifestation of a trait formed by a recessive gene, it is necessary that the offspring receive the same recessive variant of this gene from both the father and the mother (ie, in the case of homozygosity). Then, in the corresponding pair of chromosomes, both sister chromosomes will have only this one variant, which will not be suppressed by the dominant gene and can manifest itself in the phenotype.

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- This is a state of the hereditary apparatus of the body, 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.

The homozygosity of an allele is called the presence in it of two identical genes (carriers of hereditary information): either two dominant or two recessive.

Heterozygosity- this 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. Heterozygosity occurs when gametes of different quality in terms of genetic or structural composition merge into a heterozygote.

Heterozygosity is detected by analyzing crosses. Heterozygosity, as a rule, is a consequence of the sexual process, but may result from a mutation.

Allele heterozygosity is called the presence in it of two different genes, i.e. one is dominant and the other is recessive.

In addition to complete dominance, when the dominant gene overlaps the action of the recessive gene, there are known its other types:

With intermediate inheritance offspring in the 1st generation retains uniformity, but has an intermediate character. For example, when crossing a red-flowered night beauty with a white-flowered one, individuals with pink flowers were obtained in the 1st generation.

Sometimes the trait tends to lean more towards the parent with the dominant trait, this is called incomplete dominance. For example, when crossing piebald cows (white spots on the body, white belly, white legs) with bulls that have a solid color, offspring are obtained that have separate white spots - i.e. solid coloration incompletely dominates piebald.

Overdominance of hybrids manifested by heterosis - the phenomenon of the superiority of offspring over parent forms in terms of viability, fertility and productivity (such, for example, is a mule - a hybrid of a donkey and a horse).

Codominance- in a hybrid individual, both parental traits are equally manifested, this is how blood groups are inherited.

1. Autosomal dominant type of inheritance:

b. A rare trait is inherited by about half of children

in. Male and female offspring inherit this trait equally.

d. Both parents equally pass on this trait to their children.

2. Autosomal recessive type of inheritance:

b. The symptom can manifest itself in children in the absence of it in the parents. Found then in 25% of cases in children

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

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

e. Male and female offspring inherit this trait equally.

3. Inheritance linked to the X chromosome, if the gene that controls the manifestation of the trait is recessive:

a. Men inherit more often than women

b. Girls inherit this trait only from their father.

in. In marriages where both spouses are healthy, children can be born with it, while it is inherited by 50% of sons and 100% of healthy daughters

d. There is an alternation of sick men in generations: where there are more of them, where there are fewer

4. Inheritance linked to the X chromosome, if the gene that controls the manifestation of the trait is dominant:

a. Men inherit less than women

b. If the trait is only in the spouse, then all children inherit it (homozygous mother), or half of the children (heterozygous mother)

in. If only from the spouse, then all females inherit

5. Inheritance linked to the Y chromosome:

Dominant and recessive genes

Imagine two homologous chromosomes. One of them is maternal, the other is paternal. Copies of genes located on the same DNA regions of such chromosomes are called allelic or simply alleles. (gr. alios - different). These copies may be the same, that is, completely identical. Then they say that the cell or organism containing them is homozygous for this pair of alleles. (gr. homos - equal, identical and zygote - paired). Sometimes, for brevity, such a cell or organism is simply called a homozygote. If the allelic genes are somewhat different from each other, then the cells or organisms containing them are called heterozygous. (gr. heteros - different).

It is very easy to understand this situation. Imagine that your dad and mom independently typed the same short note using a typewriter, and you are holding both sheets of paper with the resulting texts in your hands. Texts are allelic genes. If the parents typed accurately and without errors, both options will completely match up to the last character. So you are homozygous according to these texts. If the texts differ due to typos and inaccuracies, their owner should be considered heterozygous. Everything is simple.

An organism or cell may be homozygous for some genes and heterozygous for others. Here, too, everything is clear. If you have not one pair of sheets with a certain text, but many such pairs, each of which contains its own text, then some texts will completely coincide, while others will differ.

Now imagine that you again have two sheets of paper with texts in your hands. One text is printed perfectly, without a single mistake. The second one is exactly the same, but with a gross typo in one word or even a missing phrase. In this situation, such a modified text can be called mutant, that is, changed (lat. mutatio - change, transformation). The same is true with genes. It is generally accepted that there are "normal", "correct" genes. Geneticists call them wild-type genes. Against their exemplary background, any altered genes can be called mutant.

The word "normal" is in quotation marks in the previous paragraph for a reason. In the process of evolution, when genes are copied, which occurs in any cell division, minor changes slowly, gradually and constantly accumulate. They also occur during the formation of gametes and, thereby, are transmitted to the next generations. In the same way, with repeated consecutive rewriting by hand of a long text, new and new inaccuracies and distortions will inevitably appear in it. Historians of ancient literature are well aware of this. Therefore, it is sometimes difficult to say which version of a gene is “normal” and completely correct. However, when an obvious gross lapse occurs, it is quite obvious against the background of the original text. With this in mind, we can talk about normal and mutant genes.

How does a mutant gene behave when paired with a normal one? If the effect of the mutation is manifested in the phenotype, that is, the consequences of the presence of the mutant gene in heterozygotes can be registered as a result of any measurements or observations, then such a mutant gene is called dominant. (lat. dominus - master). It kind of "suppresses" the normal gene. As you remember, the word "dominant" in Russian means "dominating", "dominating", "standing out over everyone." They say, for example, the military: "This height dominates the entire area." If paired with a wild-type gene, the mutant gene does not show its effect in any way, the latter is called recessive. (lat. cessatio - inaction).

The manifestation of congenital diseases and the type of their inheritance in a number of generations depend mainly on whether the altered, mutant gene responsible for the occurrence of this disease will be recessive or dominant. Descriptions of many hereditary human diseases, which are later mentioned in the book, will contain a brief mention of the type of their inheritance, if such information is not in doubt.

Dominant and recessive traits in humans (for some traits, the genes that control them are indicated)

Normal pigmentation of the skin, eyes, hair

Polydactyly (extra fingers)

Normal number of fingers

Brachydactyly (short fingers)

normal finger length

Normal glucose uptake

Normal blood clotting

Round face shape (R–)

Square face shape (rr)

Round chin (K–)

Square chin (kk)

Dimpled chin (A–)

No dimple (ah)

Dimples on the cheeks (D–)

No dimples (dd)

Thin eyebrows (bb)

Eyebrows do not connect (N–)

Eyebrows connect (nn)

Long eyelashes (L–)

Short eyelashes (ll)

Pointy nose (gg)

Round nostrils (Q–)

Narrow nostrils (qq)

Loose earlobe (S–)

Conjoined earlobe (ss)

Incomplete dominance (the genes that control the trait are indicated)

Distance between eyes - T

Hair color inheritance (controlled by four genes, inherited polymerically)

Number of dominant alleles

Very light blonde

Note. Red hair color is controlled by the D gene; this trait appears if there are less than 6 dominant genes: DD - bright red, Dd - light red, dd - non-red

1. Methods for studying human heredity: genealogical, twin, cytogenetic, biochemical and population

Genealogical methods (methods of analysis of pedigrees)

Pedigree is a diagram that reflects the ties between family members. Analyzing pedigrees, they study any normal or (more often) pathological trait in the generations of people who are related.

Genealogical methods are used to determine the hereditary or non-hereditary nature of a trait, dominance or recessiveness, chromosome mapping, sex linkage, to study the mutation process. Usually, genealogical method forms the basis for conclusions in medical genetic counseling.

When compiling pedigrees, standard notation is used. The person (individual) with whom the study begins is called a proband (if the pedigree is compiled in such a way that descend from the proband to its offspring, then it is called a family tree). The offspring of a married couple is called a sibling, siblings are called siblings, cousins are called cousins, and so on. Descendants who have a common mother (but different fathers) are called consanguineous, and descendants who have a common father (but different mothers) are called consanguineous; if the family has children from different marriages, moreover, they do not have common ancestors (for example, a child from the mother’s first marriage and a child from the father’s first marriage), then they are called consolidated.

Each member of the pedigree has its own cipher, consisting of a Roman numeral and an Arabic one, denoting the generation number and the individual number, respectively, with generation numbering sequentially from left to right. With a pedigree, there should be a legend, that is, an explanation of the accepted designations. Fragments of pedigrees illustrating the inheritance of dominant and recessive traits, as well as rare traits, are given below (Fig. 2, 3).

In closely related marriages, there is a high probability K of finding the same unfavorable allele or chromosomal aberration in spouses (Fig. 4):

Here are the values of K for some pairs of relatives in monogamy:

K [parents-children]=K [siblings]=1/2;

K [grandfather-grandson]=K [uncle-nephew]=1/4;

K [cousins] = K [great-grandfather-great-grandson] = 1/8;

K [second cousins]=1/32;

K [fourth cousins] = 1/128. Usually such distant relatives within the same family are not considered.

Based on the genealogical analysis, a conclusion is made about the hereditary conditionality of the trait. For example, the inheritance of hemophilia A among the descendants of Queen Victoria of England has been traced in detail. Genealogical analysis He established that hemophilia A is a sex-linked recessive disease.

Twins Two or more children are conceived and born by the same mother at almost the same time. The term "twins" is used in relation to humans and those mammals who normally have one child (calf). There are identical and fraternal twins.

Identical (monozygous, identical) twins arise at the earliest stages of zygote cleavage, when two or four blastomeres retain the ability to develop into a full-fledged organism during isolation. Since the zygote divides by mitosis, the genotypes of identical twins, at least initially, are completely identical. Identical twins are always of the same sex and share the same placenta during fetal development.

Fraternal (dizygotic, non-identical) twins arise differently - during the fertilization of two or more simultaneously mature eggs. Thus, they share about 50% of their genes. In other words, they are similar to ordinary brothers and sisters in their genetic constitution and can be either same-sex or different-sex.

Thus, the similarity between identical twins is determined by the same genotypes and the same conditions of intrauterine development. The similarity between fraternal twins is determined only by the same conditions of intrauterine development.

The birth rate of twins in relative terms is low and is about 1%, of which 1/3 are monozygotic twins. However, in terms of the total population of the Earth, there are over 30 million fraternal and 15 million identical twins in the world.

For studies on twins, it is very important to establish the reliability of zygosity. The most accurate zygosity is determined by reciprocal transplantation of small areas of skin. In dizygotic twins, grafts are always rejected, while in monozygotic twins, transplanted pieces of skin successfully take root. Transplanted kidneys, transplanted from one of the monozygotic twins to the other, function just as successfully and for a long time.

When comparing identical and fraternal twins raised in the same environment, one can draw a conclusion about the role of genes in the development of traits. The conditions of post-natal development for each of the twins may be different. For example, monozygotic twins were separated a few days after birth and raised in different environments. Comparison of them after 20 years in many external features (height, head volume, number of grooves on fingerprints, etc.) revealed only minor differences. At the same time, the environment affects a number of normal and pathological signs.

The twin method allows you to make reasonable conclusions about the heritability of traits: the role of heredity, environment and random factors in determining certain traits of a person,

heritability - this is the contribution of genetic factors to the formation of a trait, expressed in fractions of a unit or percentage.

To calculate the heritability of traits, the degree of similarity or difference in a number of traits in twins of different types is compared.

Consider some examples illustrating the similarity (concordance) and difference (discordance) of many features (see table).

The degree of difference (discordance) in a number of neutral traits in twins

Traits controlled by a small number of genes

Tasks for independent decision on the topic:

«CHROMOSOMAL THEORY OF HEREDITY. LINKED INHERITANCE. INHERITANCE OF SEX»

THERAPEUTIC, PEDIATRIC, MEDICAL PREVENTIVE AND DENTAL FACULTIES

1. The dominant genes that control the development of a form of cataract and polydactyly are located close to each other in the same autosome. The recessive gene responsible for the development of phenylketonuria is located on a different autosome. Determine the probability of pathology in future children of a married couple: the wife has a cataract and she is heterozygous for the phenylketonuria gene; her husband has polydactyly and is also heterozygous for the phenylketonuria gene.

2. Classical hemophilia is transmitted as an X-linked recessive trait. A man with hemophilia marries a woman who does not have the disease. They have normal daughters and sons who marry non-haemophiliac individuals. Will hemophilia be found again in grandchildren, and what is the probability of the appearance of patients in the families of daughters and sons?

3 . In humans, the inheritance of albinism is not sex-linked (A - the presence of melanin in skin cells, and - the absence of melanin in skin cells - albinism), and hemophilia is sex-linked (X H - normal blood clotting, X h - hemophilia).

Determine the genotypes of the parents, as well as the possible genotypes, sex and phenotypes of children from the marriage of a dihomozygous normal woman and albino man with hemophilia for both alleles. Make a scheme for solving the problem.

4 . Hypertrichosis is transmitted through the Y chromosome, and polydactyly is transmitted as a dominant autosomal trait. In a family where the father had hypertrichosis, and the mother had polydactyly, a daughter was born normal in relation to both signs. What is the probability that the next child in this family will also be without both anomalies?

5. In humans, color blindness is caused by an X-linked recessive gene. Thalassemia is inherited as an autosomal dominant trait and occurs in two forms: severe in homozygotes and less severe in heterozygotes.

A woman with normal vision, but with a mild form of thalassemia, married to a healthy man, but color-blind, has a color-blind son with a mild form of thalassemia. What is the probability of the birth of the next son without anomalies?

6. Enamel hypoplasia (thin granular enamel, light brown teeth) is inherited as an X-linked dominant trait. In a family where both parents had enamel hypoplasia, a son was born with normal teeth. Determine the probability of having the next child with normal teeth.

7. A man suffering from color blindness and deafness married a woman who was normal in sight and hearing well. They had a son who was deaf and color blind and a daughter (color blind but with good hearing).

Determine the probability of the birth of a daughter with both anomalies in this family, if it is known that color blindness and deafness are transmitted as recessive traits, but color blindness is linked to the X chromosome, and deafness is an autosomal trait.

8. Retinitis pigmentosa (progressive narrowing of the visual field and increasing night blindness) is inherited in two ways: an autosomal dominant trait, as an X-linked recessive trait. Determine the probability of the birth of a sick child in a family where the mother is sick and heterozygous for two pairs of genes, and the father is healthy.

9. In humans, albinism is caused by a recessive gene. Anhydrotic ectodermal dysplasia is transmitted as an X-linked recessive trait. A married couple, normal in both ways, had a son with both anomalies. What is the probability that their second child will be a girl who is normal in both ways?

10. In the Malaysian macaque, greed dominates generosity and is inherited as a dominant autosomal trait, while kleptomania (the tendency to steal) is inherited as an X-linked recessive trait.

What offspring should be expected from crossing a greedy, non-kleptomaniac female Malaysian macaque (diheterozygote) with a generous male kleptomaniac. What is the probability of a greedy male kleptomaniac appearing?

Practice #4 Help! 1) Determine the nucleotide sequence of the region of the mRNA molecule synthesized on the region of DNA with

nucleotide sequence ATTCACGACCCCTCTT
2) Determine the nucleotide sequence of the mRNA synthesized from the right strand of the DNA molecule fragment, if its left strand has the following sequence: AAACGAGTTGGATTCGTG
3) A fragment of the transcribed chain of the DNA molecule contains 38% guanyl nucleotides. Determine the content of cytidyl nucleotides in the corresponding mRNA molecule
4) The mRNA fragment has the following nucleotide sequence: GCAUUAGCAUCAGATSUGU. Determine the nucleotide sequence of the DNA molecule fragment from which this mRNA fragment is transcribed.
5) Indicate the sequence of nucleotides in both strands of the DNA fragment, if it is known that the mRNA synthesized in this region has the following structure:
6) The sequence of nucleotides at the beginning of the gene that stores information about the insulin protein begins like this: AAACACCTCTCTCTGTAGAC. Write down the amino acid sequence that starts the insulin chain.
7) The polypeptide consists of the following amino acids: glycine-valine-alanine-glycine-lysine-tryptophan-valine-serine-glutamic acid. Determine the structure of the DNA region encoding the given polypeptide.
9. A section of a protein molecule has the following amino acid sequence: arginine-methionine-tryptophan-histidine-arginine. Determine the possible sequences of nucleotides in the mRNA molecule.
10) Protein synthesis involved tRNA molecules with anticodons: UUG, GUC, CGU, UUC, GAU, AUC. Determine the nucleotide sequence in the DNA fragment, the amino acid sequence in the region of the synthesized protein and the purely nucleotide sequence in the DNA fragment, the amino acid sequence in the region of the synthesized protein and the number of nucleotides containing thymine, adenine, guanine and cytosine in a fragment of a DNA molecule.

Skin color in mulattoes is inherited as a cumulative polymer. At the same time, two autosomal unlinked genes respond to this trait. The son of a white woman and a black man married a white woman. Can a child from this marriage be darker than his father?

GIVEN:

A 1 - melanin A 2 - melanin

a 1 - absence a 2 - absence

DEFINE:

Can a child from this marriage be darker than his father?

DECISION:

1) P: ♀ a 1 a 1 a 2 a 2 x ♂ A 1 A 1 A 2 A 2

White Negro

G: a 1 a 2 A 1 A 2

F 1: A 1 a 1 A 2 a 2

Genotype: all heterozygous

Phenotype: 100%

medium mulattos

2) P: ♀ a 1 a 1 a 2 a 2 x ♂ A 1 a 1 A 2 a 2

G: a 1 a 2 A 1 A 2 ; A 1 a 2 ; a 1 A 2 ; a 1 a 2

F 2: A 1 a 1 A 2 a 2; A 1 a 1 a 2 a 2 ; a 1 a 1 A 2 a 2 ; a 1 a 1 a 2 a 2

Genotype: 1:1:1:1

Phenotype: 1:2:1

medium light white

ANSWER:

If the father is an average mulatto and the mother is white, the son cannot be darker than his father.

THEORETICAL RATIONALE:

This task is on the polymeric interaction of genes. In polymeric inheritance, the development of one trait is controlled by several pairs of non-allelic genes located in different pairs of homologous chromosomes. In this case, there is cumulative (quantitative, accumulative polymerization), in which the quality of a trait depends on the number of dominant genes: the more there are in the genotype, the more pronounced the phenotypic manifestation (in fact, many more genes are responsible for skin color than indicated in the task therefore, the skin color of people is very diverse).

Linked inheritance

No. 1. In humans, the locus of the Rh factor is linked to the locus that determines the shape of erythrocytes, and is located at a distance of 3 morganids from it (K. Stern, 1965). Rh-positiveness and elliptocytosis are determined by dominant autosomal genes. One of the spouses is heterozygous for both traits. At the same time, he inherited Rh-positiveness from one parent, elliptocytosis from the other. The second spouse is Rh-negative and has normal red blood cells. Determine the percentages of probable genotypes and phenotypes of children in this family.

No. 2. Cataract and polydactyly in humans are caused by dominant autosomal closely linked (i.e., not showing crossing over) genes. However, not necessarily the genes of these anomalies, but also the gene for cataract with the gene for the normal structure of the hand, and vice versa, can be linked.

1. A woman inherited cataract from her mother and polydacty from her father. Her husband is normal for both signs. What is more likely to be expected in their children of the simultaneous appearance of cataracts and polydacty, the absence of both of these signs, or the presence of only one anomaly - cataracts or polydactyly.

2. What offspring can be expected in a family where the husband is normal and the wife is heterozygous for both traits, if it is known that the wife's mother also suffered from both anomalies, and her father was normal.

3. What offspring can be expected in a family with parents heterozygous for both traits, if it is known that the mothers of both spouses suffered only from cataracts, and the fathers only from polydactyly.

No. 3. Classical hemophilia and color blindness are inherited as X-linked recessive traits. The distance between genes is definitely 9.8 morganids.

1. A girl whose father suffers from both hemophilia and color blindness, and whose mother is healthy and comes from a family prosperous for these diseases, marries a healthy man. Determine the likely phenotypes of children from this marriage.

2. A woman whose mother was colorblind and her father was hemophilia marries a man with both conditions. Determine the probability of having children in this family at the same time with both anomalies.

No. 4. The gene for color blindness and the gene for night blindness, inherited through the X chromosome, are located at a distance of 50 morganids from each other (K. Stern, 1965). Both traits are recessive.

1. Determine the probability of having children at the same time with both anomalies in a family where the wife has normal vision, but her mother suffered from night blindness, and her father suffered from color blindness, while the husband is normal in relation to both signs.

2. Determine the probability of having children simultaneously with both anomalies in a family where the wife is heterozygous for both traits and inherited both anomalies from her father, and the husband has both forms of blindness.

No. 5. The dominant genes for cataract and elliptocytosis are located in the first autosome. Determine the probable phenotypes and genotypes of children from the marriage of a healthy woman and a diheterozygous man. There is no crossover.

No. 6. The distance between genes C and D is 4.6 morganides. Determine the % of gametes of each type: CD, cd, Cd and cD produced by a diheterozygous organism.

No. 7. The genes that control sickle cell anemia and b-thalassemia in humans are recessive, closely linked on chromosome C. The husband and wife are diheterozygous and inherit both mutant alleles from different parents. Determine the relative likelihood of developing these hereditary diseases for their future children.

No. 8. The genes that control leukodystrophy, methemoglobinemia and one of the forms of ocular albinism in humans are located on chromosome 22. Leukodystrophy and ocular albinism are recessive traits, methemoglobinemia is dominant. Determine the relative probability of developing future children of the following couples for hereditary diseases: a) the husband and wife are healthy; the husband inherited the genes of leukodystrophy and ocular albinism from his father, the wife received the same genes from two parents; b) the husband inherited the gene of methemoglobinemia from his father, and the gene of ocular albinism from his mother; the wife is healthy and heterozygous for the genes of albinism and leukodystrophy.

No. 9. The genes that affect the presence of the Rh factor and the shape of red blood cells are located in the same autosome at a distance of 3 morganids. The woman received from her father the dominant gene Rh, which determines Rh-positiveness, and the dominant gene E, which determines the elliptical shape of erythrocytes, and from the mother, the recessive genes for Rh-negativity rh and the normal shape of erythrocytes (e). Her husband is Rh-negative and has a normal form of red blood cells. Determine the probability of the birth of a child phenotypically similar in these signs: a) with the mother; b) with his father.

No. 10. A man received from his father a dominant Rh-positive gene Rh and a recessive gene that determines the normal shape of erythrocytes (e), and from his mother - a recessive Rh-negative gene rh and a dominant E gene that causes the formation of elliptical erythrocytes. His wife is Rh-negative, with normal red blood cells. What is the probability (in percent) that the child will be similar to the father in these characteristics?

No. 11. A woman received from her mother an autosome with a dominant gene that causes a defect in the nails and patella, and a gene that determines blood group A. The homologous chromosome contains a recessive gene that does not affect the patella, and a gene for blood group I. The distance between genes is 10 morganids. The husband has a normal patella and no nail defect and homozygous blood group III. Determine the possible phenotypes in the offspring of this family.

Algorithm for solving problem No. 2.

Cataracts and polydactyly in humans are caused by dominant autonomic closely linked (i.e., not showing crossing over) genes. However, the genes of these anomalies may not necessarily be linked, but also the cataract gene with the gene for the normal structure of the hand and vice versa:

a) the woman inherited cataracts from her mother, and
polydactyly - from the father, her husband is normal in relation to both signs.
What is more likely to be expected in her children: the simultaneous manifestation
cataracts and polydactyly, the absence of both of these signs or
the presence of only one anomaly?

b) what offspring can be expected in a family where the husband is normal, and
the wife is heterozygous for both traits, if it is known that the wife's mother also suffered from both anomalies, and her father was normal;

c) what offspring can be expected in the family of parents
heterozygous for both traits, if it is known that the mothers of both
spouses suffered only cataracts, and fathers - polydactyly?

DEFINE:

F 1 - in each family

DECISION:

1. Let's write down the scheme of marriage of a woman who inherited a cataract from her mother, polydactyly from her father with a man who is normal in both respects.

ANSWER:

If a woman inherits cataracts from one of her parents (from her mother), and polydactyly from her father, and her husband is normal in both signs, then from this marriage 50% of children can be with polydactyly and 50% with cataracts.

2. Let's write down the scheme of marriage of a woman, diheterozygous (both anomalies from the mother) with a man, normal in relation to both traits.

ANSWER:

If a woman is heterozygous for both traits, and she inherited both abnormal genes from her mother, and a man is normal for both traits, then 50% of their children from their marriage will have both anomalies (both polydactyly and cataracts), and 50% will have healthy in relation to these pathologies.

3. Let's write down the scheme of marriage of parents who are heterozygous for both traits, given that the mothers of both spouses suffered only from cataracts, and the fathers from polydactyly.

ANSWER:

If the parents are heterozygous for both traits, given that the mothers of both spouses suffered only cataracts, the fathers - polydactyly, then 25% of the children from this marriage will suffer from cataracts, 25% - polydactyly, and 50% of children will show both anomalies.

THEORETICAL RATIONALE:

The task of Morgan's law of linked inheritance is that genes located on the same chromosome are inherited linked.

Algorithm for solving problem No. 11.

The woman received from her mother an autosome with a dominant gene that causes a defect in the nails and patella, and a gene that determines blood type A. The homologous chromosome contains a recessive gene that does not affect the patella and the nature of the nails, and the I blood group gene. The distance between genes is 10 morganids. The husband has a normal patella and no nail defect and homozygous blood group III. Determine possible phenotypes in the offspring of this family

GIVEN:

A - syndrome of defect of nails and patella

a - norm

i - the first blood group

J A - second blood type

J B - third blood type

J A, J B - fourth blood type

DEFINE:

Phenotypes F 1

DECISION:

Possible clutch groups:

I , J A , J B i , J A , J B

2.1. Dihybrid cross

1. It is known that the gene for six-fingeredness (one of the varieties of polydactyly), as well as the gene that controls the presence of freckles, are dominant genes located in different pairs of autosomes.

A woman with a normal number of fingers on her hands and with freckles on her face marries a man who also has five fingers on each hand, but not from birth, but after undergoing childhood surgery to remove the sixth finger on each hand. There were no freckles on the man's face from birth, and there are none at the present time. This family has an only child: five-fingered, like his mother, and without freckles, like his father. Calculate what chance these parents had to create just such a child.

Decision . Let us designate the genes under consideration by letters of the Latin alphabet, compile the table "Gene-trait" (Table 1) and the crossover scheme (Scheme 1).

In this case, the genotype of a man (relative to the number of fingers on his hands) should be written as Ah, because the operation to remove an extra finger only affected the appearance of this person’s hand, but not his genotype, which probably includes the six-fingered gene BUT-.
The appearance of a five-fingered child in the family undoubtedly indicates that the genotype of this man is heterozygous. Otherwise, he could not have had a five-fingered descendant, which, undoubtedly, is one gene a received from his mother, and the second - from his father (who did not manifest himself in the phenotype of the father himself), which allowed the child to become the happy owner of the genotype ah, in the presence of which a person will certainly have 5 fingers on each hand.
It is not difficult to determine what the gametes of the parents will look like, which is fixed, on the one hand, in the crossing scheme on the line G, on the other hand, in the Punnett lattice (Table 2), when analyzing the data of which it turns out that the probability of these parents having a child with the genotype aa bb(five-fingered, no freckles) was 25%.

2. It is known that cataracts and red hair in humans are controlled by dominant genes located in different pairs of autosomes. A red-haired woman with no cataracts married a fair-haired man who recently had cataract surgery.
Determine what children can be born to these spouses, assuming that the man's mother has the same phenotype as his wife (i.e. she is red-haired and does not have cataracts).

Decision . We compile the table "Gene-feature" (Table 3) and the crossover scheme (Scheme 2).

In order to solve this problem, one can compose a Punnett lattice (Table 4).

Therefore: 1/4 of the offspring are similar to the mother;
1/4 of the children - to the father (according to the two criteria under consideration);
1/4 - red-haired, like a mother, but with a cataract, like a father;
1/4 are fair-haired, like their father, and without cataracts, like their mother.

3. A diabetic woman (her parents had normal carbohydrate metabolism), an Rh-positive (her mother is also Rh-positive, while her father is Rh-negative), and a non-diabetic man (his mother was a pronounced diabetes mellitus), Rh-positive (his father was Rh-negative), a child was born: Rh-negative, suffering from diabetes since childhood.
What chances did the child have of appearing just like that, given all the information at our disposal about the close and distant relatives of this child? The Rh-positive gene is a dominant gene (as is the gene that controls normal carbohydrate metabolism).

Decision . Based on the data contained in the condition of this task, we compile the table "Gene-trait" (Table 5) and the crossover scheme (Scheme 3).

In order to answer the question contained in the condition of the problem, in this case it is better to use the first method, namely: to make two monohybrid crosses (schemes 4 and 5) and, guided by theoretical training, say what is the probability of a mono-morecessive combination in each of the monohybrid crosses; then multiply the obtained probabilities and get the probability of the appearance of a digomorecessive.
It is easy to consider in the first monohybrid cross (Scheme 4) one of the variants of the usual analyzing cross ( aa X Ah), at which the probability of occurrence of a monogorecessive aa= 1/2.

And in the second monohybrid crossing (Scheme 5), we have G. Mendel's II law, from which it follows that when crossing Rhrh X Rhrh(two heterozygotes) the probability of occurrence of a mono-recessive rhrh = 1/4.
Multiplying the obtained probabilities, we get the final answer:

4. One of the spouses has ll blood group, is Rh-negative. His mother, like him, has type II blood and is Rh-negative. His father also has ll blood type, but he is Rh-positive. The second spouse is with lV blood group, Rh-positive. There is the following information about his parents: one of them is with lV blood group and is Rh-positive, the other is with lll blood group and is Rh-negative. Determine the probability of occurrence in this family of all options genotypes of children, taking into account that we are talking about blood groups (ABO system) and that the Rh gene is dominant, and the rh gene is recessive.

Answer. Rh-positive children: from ll gr. blood - 3/8; with lll gr. blood - 3/16; with lV gr. blood - 3/16; total - 3/4. Rh-negative children: from ll gr. blood - 1/8; with lll gr. blood - 1/16; with lV gr. blood - 1/16; total - 1/4.

5. In the family of parents who have developed the ability to absorb the amino acid phenylalanine, but have a visual defect - myopia, two children are born: one child is myopic, like his parents, but with no phenylketonuria disease; the second - with normal vision, but suffering from phenylketonuria.
To determine what are the chances for children born in this family to be exactly the same if it is known that the development of myopia is controlled by a dominant gene, and the presence of a disease such as phenylketonuria is controlled by a recessive gene, and both pairs of genes are located in different pairs of autosomes.

Answer. Children with normal vision (not myopic), but with phenylketonuria - 1/16; myopic, but without phenylketonuria - 9/16.

6. From the marriage of a red-haired woman with cheerful freckles on her face and a black-haired man who does not have freckles, a child appeared, whose genotype can be written as a dihomorecessive. Determine the genotypes of the child's parents, the phenotype of the offspring itself and the probability of the appearance of such a child in this family.

Answer. Red-haired children, without freckles - 25%.

To be continued

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

Types of inheritance of traits in humans

Monogenic inheritance

Signs of autosomal dominant inheritance

Autosomal dominant traits

Autosomal recessive inheritance pattern

Type of inheritance linked to the X chromosome

Autosomal dominant diseases

Polygenic inheritance

See what a "recessive gene" is in other dictionaries:

Polydactyly and cataract are autosomal dominant

Other questions from the category

Dominant and recessive genes;

Dominant and recessive genes

Dominant and recessive traits in humans (for some traits, the genes that control them are indicated)

Incomplete dominance (the genes that control the trait are indicated)

Hair color inheritance (controlled by four genes, inherited polymerically)

1. Methods for studying human heredity: genealogical, twin, cytogenetic, biochemical and population

2.1. Dihybrid cross