Morgan's law. Complete and incomplete linkage of genes. The concept of genetic maps of chromosomes. Chromosomal theory of heredity. sex-linked inheritance

Opened by G.T. Morgan and his students in 1911-1926. They proved that Mendel's III law requires additions: hereditary inclinations are not always inherited independently, sometimes they are transmitted in whole groups - they are linked to each other. The established patterns of the location of genes in chromosomes contributed to the elucidation of the cytological mechanisms of the laws of Gregor Mendel and the development of the genetic foundations of the theory natural selection. Such groups can move to another homologous chromosome when conjugated during prophase 1 of meiosis.

Provisions of the chromosome theory:

• 1) Transfer hereditary information associated with chromosomes, in which genes lie linearly, at certain loci.
• 2) Each gene of one homologous chromosome corresponds to an allelic gene of another homologous chromosome.
• 3) Allelic genes can be the same in homozygotes and different in heterozygotes.
• 4) Each individual in the population contains only 2 alleles, and gametes - one allele.
• 5) In the phenotype, the trait manifests itself in the presence of 2 allelic genes.
• 6) The degree of dominance in multiple alleles increases from extreme recessive to extreme dominant. For example, in a rabbit, coat color depends on the recessive gene "c" - the gene for albinism. Dominant in relation to "c" will be the gene "ch "" - Himalayan (ermine) color - white body, single eyes, dark tips of the nose, ears, tail and limbs. Dominant in relation to "ch" will be the "chc" gene - chinchilla - light gray. Even more dominant will be the “sa” gene - agouti, dark in color. The most dominant gene will be C - black in color, it dominates all alleles - C, ca, chc, ch, s.
• 7) Dominance and recessiveness of alleles are not absolute, but relative. The same trait can be inherited in a dominant OR recessive manner. For example, the inheritance of epicanthus in Negroids is dominant, in Mongoloids it is recessive, in Caucasians this allele is absent. Newly emerging alleles are recessive. The old ones are dominant.
• 8) Each pair of chromosomes is characterized by a certain set of genes that make up linkage groups, often inherited together.
• 9) The number of linkage groups is equal to the number of chromosomes in the haploid set.
• 10) The movement of genes from one homologous chromosome to another in prophase 1 of meiosis occurs at a certain frequency, which is inversely proportional to the distance between the genes - the smaller the distance between the genes, the greater the adhesion force between them, and vice versa.
• 11) The unit of distance between genes is the morganide, which is equal to 1% of crossover offspring. For example, the gene for the Rh factor and the gene for ovalocytosis are located 3 morganids apart, and the gene for color blindness and hemophilia is 10 morganids apart.

The provisions of the chromosome theory were proved cytologically and experimentally by Morgan on the fruit fly Drosophila.

The inheritance of traits whose genes are located on the X and Y sex chromosomes is called sex-linked inheritance. For example, in humans, the recessive genes for color blindness and hemophilia are located on the X sex chromosome. Consider the inheritance of hemophilia in humans:

h - gene for hemophilia (bleeding);

H - gene for normal blood clotting.

The recessive trait is manifested in boys, in girls it is suppressed by the allelic dominant H-gene.

Inheritance of a trait occurs crosswise - from sex to sex, from mother to sons, from father to daughters.

The external manifestation of a trait - the phenotype - depends on several conditions:

• 1) the presence of 2 hereditary deposits from both parents;
• 2) on the way of interaction between allelic genes (dominant, recessive, co-dominance);
• 3) on the conditions of interaction between non-allelic genes (complementary, epistatic interaction, polymerism, pleiotropy);
• 4) from the location of the gene (in the autosome or sex chromosome);
• 5) from environmental conditions.

Chromosomal theory heredity formulated in 1911-1926. T. H. Morgan based on the results of his research. With its help, the material basis of the laws of heredity established by G. Mendel was clarified, and why, in certain cases, the inheritance of certain traits deviates from them.

Key points

Main provisions chromosomal theories of heredity such:

• genes are arranged in a linear order on chromosomes;
• different chromosomes have different sets of genes, i.e. each of the non-homologous chromosomes has its own unique set of genes;
• each gene occupies a certain area in the chromosome; allelic genes occupy the same regions in homologous chromosomes;
• all genes of one chromosome form a linkage group, due to which some traits are inherited linked; the strength of linkage between two genes located on the same chromosome is inversely proportional to the distance between them;
• the linkage between the genes of one group is broken due to the exchange of sections of homologous chromosomes in the prophase of the first meiotic division (the process of crossing over)
• everyone species characterized by a certain set of chromosomes (karyotype) - the number and structural features of individual chromosomes.

Chromosomal theory of heredity, the theory according to which the chromosomes enclosed in the cell nucleus are carriers of genes and is the material basis of heredity, that is, the continuity of the properties of organisms in a number of generations is determined by the continuity of their chromosomes.

Story

The chromosome theory of heredity arose at the beginning of the 20th century on the basis of cell theory and the use of hybridological analysis to study the hereditary properties of organisms.

In 1902, W. Setton in the USA drew attention to the parallelism in the behavior of chromosomes and the so-called Mendel. "Hereditary factors", and T. Boveri in Germany put forward the chromosomal hypothesis of heredity, according to which Mendel's hereditary factors (later called genes) are localized in chromosomes. The first confirmation of this hypothesis was obtained in the study of the genetic mechanism of sex determination in animals, when it was found that this mechanism is based on the distribution of sex chromosomes among the offspring. Further substantiation of H. t belongs to the American geneticist T. H. Morgan, who noted that the transfer of certain genes (for example, the gene that causes white-eyed female Drosophila when crossed with red-eyed males) is associated with the transfer of the sexual X chromosome, that is, traits are inherited, sex-linked (in humans, several dozen such signs are known, including some hereditary defects - color blindness, hemophilia, etc.).

Evidence for the theory was obtained in 1913 by the American geneticist K. Bridges, who discovered chromosome nondisjunction during meiosis in female Drosophila and noted that disturbances in the distribution of sex chromosomes are accompanied by changes in the inheritance of sex-linked traits.

With the development of the theory, it was found that genes located on the same chromosome constitute one linkage group and must be inherited together; the number of linkage groups is equal to the number of pairs of chromosomes, which is constant for each type of organism; traits that depend on linked genes are also inherited together. As a result, the law of independent combination of features should have limited application; traits whose genes are located on different (non-homologous) chromosomes must be inherited independently. The phenomenon of incomplete linkage of genes (when, along with parental combinations of traits, new recombinant traits are found in the offspring from crossings, their combination) was studied in detail by Morgan and his colleagues (A. G. Sturtevant and others) and served as a justification for the linear arrangement of genes in chromosomes. Morgan suggested that the linked genes of homologous chromosomes that are in combinations in parents and, in meiosis in the heterozygous form ® can change places, resulting in the formation of gametes Ab and ab next to the gametes AB and ab. Such recombinations occur due to breaks in homologous chromosomes in the area between genes and the further connection of the broken ends in a new combination: The reality of this process, called the intersection of chromosomes, or crossing over, was proved in 1933 by him, the scientist K. Stern in experiments with Drosophila and American scientists H. Creightonomi B. McClintock - with corn. The farther apart the linked genes are, the more likely they are to cross over. The dependence of the frequency of crossing over on the distances between linked genes was used to construct genetic maps of chromosomes. In the 30s. 20 in F. Dobzhansky showed that the order of placement of genes on genetic and cytological maps of chromosomes coincides.

According to the ideas of the Morgan school, genes are discrete and further indivisible carriers of hereditary information. However, the discovery in 1925 by the Soviet scientists G. A. Nadson and G. S. Filippov, and in 1927 by the American scientist R. Meller of the influence x-rays on the occurrence of hereditary changes (mutations) in Drosophila, as well as the use of X-rays to accelerate the mutation process in Drosophila, allowed Soviet scientists A. S. Serebrovsky, N. P. Dubinin and others to formulate 1928-30 ideas about the divisibility of a gene into smaller units arranged in a linear sequence and capable of mutational changes. In 1957, these ideas were completed by the work of the American scientist S. Benzer with the T4 bacteriophage. The use of X-rays to stimulate chromosomal rearrangements made it possible for N. P. Dubinin and B. N. Sidorov to discover in 1934 the effect of the position of a gene (discovered in 1925 by Sturtevant), that is, the dependence of the manifestation of a gene on its location on the chromosome. There was an idea of ​​the unity of discreteness and continuity in the structure of the chromosome.

The chromosome theory of heredity is developing in the direction of deepening knowledge about the universal carriers of hereditary information - the deoxyribonucleic acid (DNA) molecule. It has been established that a continuous sequence of purine and pyrimidine bases along the DNA chain (deoxyribonucleic acid) forms genes, intergene intervals, signs of the beginning and end of reading information within a gene; determines the hereditary nature of the synthesis of specific cell proteins and, consequently, the hereditary nature of metabolism. DNA (deoxyribonucleic acid) forms the material basis of the linkage group in bacteria and many viruses (in some viruses, ribonucleic acid is the carrier of hereditary information). material carriers cytoplasmic inheritance.

H. t. N., Explaining the patterns of inheritance of traits in animals and plant organisms, plays an important role in page - x. (agricultural) science and practice. It equips breeders with methods for breeding animal breeds and plant varieties with desired properties. Some positions X. t allow to conduct page - x more rationally. (agricultural) production. So, the phenomenon of the inheritance of a number of signs linked to a floor in page - x. (agricultural) animals allowed before the invention of methods of artificial regulation of sex in silkworm to cull cocoons of a less productive sex, to the development of a method for separating chickens by sex by examining the cloaca—to cull cockerels, and so on. (agricultural) crops has the use of polyploidy. The study of hereditary diseases person.

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The creator of the chromosome theory (CT) is the scientist Thomas Morgan. CHT is the result of studying heredity at the cellular level.

The essence of the chromosome theory:

Chromosomes are the material carriers of heredity.

The main evidence for this is:

Cytogenetic parallelism

Chromosomal sex determination

sex-linked inheritance

Gene linkage and crossing over

The main provisions of the chromosome theory:

Hereditary inclinations (genes) are localized in chromosomes.

Genes are located on the chromosome in a linear order.

Each gene occupies a specific area (locus). Allelic genes occupy similar loci on homologous chromosomes.

Genes located on the same chromosome are inherited together, linked (Morgan's Law) and form a linkage group. The number of linkage groups is equal to the haploid number of chromosomes (n).

Between homologous chromosomes, an exchange of regions, or recombination, is possible.

The distance between genes is measured in percent of crossing over - morganides.

The frequency of crossing over is inversely proportional to the distance between genes, and the strength of linkage between genes is inversely proportional to the distance between them.

Cytogenetic parallelism

Morgan's graduate student Sutton noticed that the behavior of genes according to Mendel coincides with the behavior of chromosomes: (TABLE - Cytogenetic Parallelism)

Each organism carries 2 hereditary inclinations, only 1 hereditary inclination from a pair enters the gamete. During fertilization in the zygote and further in the body, again 2 hereditary inclinations for each trait.

Chromosomes behave in exactly the same way, which suggests that genes lie on chromosomes and are inherited along with them.

Chromosomal sex determination

In 1917, Allen showed that male and female mosses differ in the number of chromosomes. In cells of diploid tissue male body sex chromosomes X and Y, in female X and X. Thus, chromosomes determine such a trait as sex, and therefore can be material carriers of heredity. Later, chromosomal sex determination was also shown for other organisms, including humans. (TABLE)

sex-linked inheritance

Since the sex chromosomes are different in male and female organisms, traits whose genes are located on the X or Y chromosomes will be inherited differently. Such signs are called sex-linked traits.

Features of the inheritance of sex-linked traits

Mendel's 1st law is not respected

Reciprocal crosses give different results

There is a criss-cross (or criss-cross inheritance).

For the first time, inheritance associated with a trait was discovered by Morgan in Drosophila.

(TABLE sex-linked inheritance)

Sex-linked inheritance is explained by the absence of genes on the Y chromosome that are allelic to genes on the X chromosome. The Y chromosome is much smaller than the X chromosome, it currently contains 78 (?) genes, while there are more than 1098 on the X chromosome.

Examples of sex-linked inheritances:

Hemophilia, Duchenne dystrophy, Duncan's syndrome, Alport's syndrome, etc.

There are genes that, on the contrary, are found on the Y chromosome and are absent on the X chromosome; therefore, they are found only in male organisms, and never in female organisms (Holandric inheritance) and are transmitted only to sons from the father.

Gene linkage and crossing over

In genetics, such a phenomenon as "gene attraction" was known: some non-allelic traits were not inherited independently, as they should according to Mendel's III law, but were inherited together, did not give new combinations. Morgan explained this by saying that these genes are on the same chromosome, so they diverge into daughter cells together in one group, as if linked. He called this phenomenon linked inheritance.

Morgan's Coupling Law:

Genes located on the same chromosome are inherited together, linked.

Genes located on the same chromosome form a linkage group. The number of linkage groups is equal to "n" - the haploid number of chromosomes.

Crossed homozygous lines of flies with a gray body color and long wings and flies with black body and short wings. The genes for body color and wing length are linked, i.e. lie on the same chromosome.

As a result, in F 2, splitting occurs as in a 3: 1 monohybrid cross.

Crossing over.

In a small percentage of cases in F 2 in Morgan's experiments, flies appeared with new combinations of characters: long wings, black body; the wings are short and the body is grey. Those. the signs "disconnected". Morgan explained this by the fact that chromosomes exchange genes during conjugation in meiosis. As a result, individuals with new combinations of traits are obtained, i.e. as required by Mendel's third law. Morgan called this gene exchange recombination.

Later, cytologists did indeed confirm Morgan's hypothesis by discovering the exchange of chromosome regions in corn and in the salamander. They called this process crossing over.

Crossing over increases the diversity of offspring in a population.

The mechanism of inheritance of linked genes, as well as the location of some linked genes, was established by the American geneticist and embryologist T. Morgan. He showed that the law of independent inheritance formulated by Mendel is valid only in cases where genes carrying independent traits are localized on different non-homologous chromosomes. If the genes are on the same chromosome, then the inheritance of traits occurs jointly, that is, linked. This phenomenon came to be called linked inheritance, as well as the law of linkage or Morgan's law.

The law of bonding says: linked genes located on the same chromosome are inherited together (linked). clutch group All genes on one chromosome. The number of linkage groups is equal to the number of chromosomes in the haploid set. For example, a person has 46 chromosomes - 23 linkage groups, a pea has 14 chromosomes - 7 linkage groups, a fruit fly Drosophila has 8 chromosomes - 4 linkage groups. Incomplete linkage of genes- the result of crossing over between linked genes, That's why complete linkage of genes possibly in organisms in whose cells crossing over does not normally occur.

MORGAN'S CHROMOSOMAL THEORY. MAIN PROVISIONS.

The result of T. Morgan's research was the creation of the chromosome theory of heredity:

1) genes are located on chromosomes; different chromosomes contain an unequal number of genes; the set of genes for each of the nonhomologous chromosomes is unique;

2) each gene has certain place(locus) on a chromosome; allelic genes are located in identical loci of homologous chromosomes;

3) genes are located on chromosomes in a certain linear sequence;

4) genes located on the same chromosome are inherited together, forming a linkage group; the number of linkage groups is equal to the haploid set of chromosomes and is constant for each type of organism;

5) linkage of genes can be disturbed during the process of crossing over, which leads to the formation of recombinant chromosomes; the frequency of crossing over depends on the distance between genes: the greater the distance, the greater the value of crossing over;

6) each species has a set of chromosomes characteristic only for it - a karyotype.

sex-linked inheritance- this is the inheritance of a gene located on the sex chromosomes. With heredity associated with the Y chromosome, the trait or disease manifests itself exclusively in the male, since this sex chromosome is absent in chromosome set women. The inheritance associated with the X chromosome can be dominant or recessive in the female body, but it is always present in the male, since there is only one X chromosome. Sex-linked inheritance of the disease is associated mainly with the sex X chromosome. Most hereditary diseases (certain pathological signs) associated with sex are transmitted recessively. There are about 100 such diseases. A woman carrying a pathological trait does not suffer herself, since a healthy X chromosome dominates and suppresses the X chromosome with a pathological trait, i.e. compensates for the inferiority of this chromosome. In this case, the disease manifests itself only in males. According to the recessive X-linked type, the following are transmitted: color blindness (red-green blindness), optic nerve atrophy, night blindness, Duchenne myopia, "curly hair" syndrome (results from a violation of copper metabolism, an increase in its content in tissues, manifests itself as weakly colored , sparse and falling hair, mental retardation, etc.), a defect in enzymes that convert purine bases into nucleotides (accompanied by impaired DNA synthesis in the form of Lesch-Nyen syndrome, manifested by mental retardation, aggressive behavior, self-harm), hemophilia A (as a result of a lack of antihemophilic globulin - factor VIII), hemophilia B (as a result of a deficiency of the Christmas factor - factor IX), etc. According to the dominant X-linked type, hypophosphatemic rickets (not treatable with vitamins D2 and D3), brown tooth enamel, etc. are transmitted. These diseases develop in both males and females.

Complete and incomplete linkage of genes.

Genes on chromosomes have different strength clutch. Linkage of genes can be: complete, if recombination between genes belonging to the same linkage group is impossible and incomplete, if recombination is possible between genes belonging to the same linkage group.

Genetic maps of chromosomes.

These are diagrams of the relative arrangement of interconnected

hereditary factors - genes. G. k. x. display realistically

the existing linear arrangement of genes on chromosomes (see Cytological maps of chromosomes) and are important both in theoretical studies, and during selection work, because make it possible to consciously select pairs of traits during crosses, as well as to predict the features of inheritance and the manifestation of various traits in the studied organisms. Having G. to. x., it is possible, by inheritance of a “signal” gene, closely linked to the one under study, to control the transmission to offspring of genes that determine the development of hard-to-analyze traits; for example, the gene that determines the endosperm in corn and is located on the 9th chromosome is linked to the gene that determines the reduced viability of the plant.

85. Chromosomal mechanism of sex inheritance. Cytogenetic methods for determining sex.

Floor characterized by a set of features determined by genes located on chromosomes. In species with dioecious individuals, the chromosome complex of males and females is not the same, cytologically they differ in one pair of chromosomes, it was called sex chromosomes. The identical chromosomes of this pair are called X (x) - chromosomes . Unpaired, absent in the other sex Y (y) - chromosome ; the rest, for which there are no differences autosomes(BUT). Humans have 23 pairs of chromosomes. Of them 22 pairs of autosomes and 1 pair of sex chromosomes. Sex with the same XX chromosomes, forming one type of gamete (with an X chromosome), is called homogametic other gender, different chromosomes XY, which forms two types of gametes (with an X chromosome and with a Y chromosome), - heterogametic. In humans, mammals and other organisms male heterogametic sex; in birds, butterflies - female.

X chromosomes, in addition to the genes that determine female, contain genes that are not related to sex. Traits determined by chromosomes are called sex-linked traits. In humans, such signs are color blindness (color blindness) and hemophilia (blood incoagulability). These anomalies are recessive; in women, such signs do not appear, even if these genes are carried by one of the X chromosomes; such a woman is a carrier and passes them on with the X chromosome to her sons.

Cytogenetic method for sex determination. It is based on the microscopic examination of chromosomes in human cells. The use of cyto genetic method allows not only to study the normal morphology of chromosomes and the karyotype as a whole, to determine the genetic sex of the organism, but, most importantly, to diagnose various chromosomal diseases associated with a change in the number of chromosomes or with a violation of their structure. As an express method that detects a change in the number of sex chromosomes, use method for determining sex chromatin in non-dividing cells of the buccal mucosa. Sex chromatin, or Barr body, is formed in cells female body one of the two X chromosomes. With an increase in the number of X - chromosomes in the karyotype of an organism, Barr bodies are formed in its cells in an amount one less than the number of chromosomes. With a decrease in the number of chromosomes, the body is absent. In the male karyotype, the Y-chromosome can be detected by a more intense luminescence compared to other chromosomes when treated with acrichiniprite and studied in ultraviolet light.

Features of the structure of chromosomes. Levels of organization of hereditary material. Hetero- and euchromatin.

Morphology of chromosomes

In the microscopic analysis of chromosomes, first of all, their differences in shape and size are visible. The structure of each chromosome is purely individual. It can also be seen that chromosomes have common morphological features. They are made up of two strands. - chromatid, located in parallel and interconnected at one point, called the centromere or primary constriction. On some chromosomes, a secondary constriction can also be seen. She happens to be hallmark to identify individual chromosomes in a cell. If the secondary constriction is located close to the end of the chromosome, then the distal region bounded by it is called a satellite. Chromosomes containing a satellite are referred to as AT chromosomes. On some of them, the formation of nucleoli occurs in telophase.
The ends of chromosomes have special structure and are called telomeres. Telomere regions have a certain polarity that prevents them from connecting to each other when broken or with the free ends of chromosomes.

The section of the chromatid (chromosome) from the telomere to the centromere is called the arm of the chromosome. Each chromosome has two arms. Depending on the ratio of the lengths of the arms, three types of chromosomes are distinguished: 1) metacentric (equal arms); 2) submetacentric (unequal shoulders); 3) acrocentric, in which one shoulder is very short and not always clearly distinguishable. (p - short arm, q - long arm). The study of the chemical organization of chromosomes of eukaryotic cells showed that they consist mainly of DNA and proteins: histones and protomite (in germ cells), which form a nucleoprotein complex-chromatin, which received its name for the ability to stain with basic dyes. Proteins make up a significant part of the substance of chromosomes. They account for about 65% of the mass of these structures. All chromosomal proteins are divided into two groups: histones and nonhistone proteins.
Histones represented by five fractions: HI, H2A, H2B, H3, H4. Being positively charged basic proteins, they are quite firmly attached to DNA molecules, which prevents the biological information contained in it from being read. This is their regulatory role. In addition, these proteins perform a structural function, providing the spatial organization of DNA in chromosomes.

Number of fractions nonhistone proteins exceeds 100. Among them are enzymes for the synthesis and processing of RNA, reduplication and DNA repair. Acidic proteins of chromosomes also play a structural and regulatory role. In addition to DNA and proteins, RNA, lipids, polysaccharides, and metal ions are also found in the chromosomes.

The chromosome theory of heredity is based on the knowledge of scientists about the structure of genes and their transmission to the next generations. This makes it possible to answer some questions related to our origin, external data, behavior, diseases, etc. The chromosome theory of heredity is the order in which the information contained in the genes is transmitted from parents to children, which in total give a new person.

Heredity

Information is inherited through thousands of genes that are in the nuclei of the egg and sperm that form a new organism. Each gene has a code that synthesizes one certain kind squirrel. This process is streamlined, which makes it possible to predict the characteristics of the future generation. This is because genes (the units of inheritance) are combined in a certain order. An interesting fact remains that each cell contains a pair of chromosomes responsible for one protein. Thus, each gene is paired (allelic). One of them dominates, the other is in a "sleeping" state. This is inherent in all cells of the body, except for the sex cells (they have only one DNA strand to form a full-fledged nucleus with a full set of chromosomes during fusion into a zygote). These simple truths and are called the "chromosome theory of heredity", or Mendel's genetics.

Offspring

During the formation of gametes, pairs of genes diverge, but during fertilization, something else happens: the genes of the egg and sperm are combined. The new combination makes it possible to reveal the development of certain traits in offspring. Since each parent has allelic genes, they cannot predict which ones will be passed on to the child. Of course, according to one of Mendel's laws, dominant genes are stronger, and therefore it is likely that they will appear in a child, but it all depends on the case.

Diseases

Human chromosomes are 23 pairs. Sometimes the set may be incorrect as a result of the attachment of an extra gene. Then various kinds of mutations can occur. It is also called "chromosomal syndrome" - a change in the structure of the DNA chain: chromosome inversion, its loss, duplication, rearrangement in a certain area. It is also possible to exchange sections of dissimilar chromosomes, rearrange a certain section, or transfer a gene from one chromosome to another. Vivid examples of such manifestations are the following diseases.

1. Syndrome "cat's cry"

The chromosomal theory of heredity confirms that such a violation is caused by the loss of a short arm of the fifth chromosome. This ailment manifests itself in the first minutes of life in the form of crying, similar to a cat's "meow". After a few weeks, this symptom disappears. How older child, the more clearly the abnormal development is visible: at first it is distinguished by its low weight, then the asymmetry of the face is more and more clearly visible, microcephaly appears, the eyes are slanted, the bridge of the nose is wide, abnormal ears with an external auditory canal, heart disease is possible. Physical and mental retardation is an integral part of the disease.

• Aneuploidy(not a multiple of the haploid set of chromosomes). A striking example- Edwards syndrome. Manifested by childbirth early dates, the fetus has skeletal muscle hypoplasia, low weight, microcephaly. The presence of a "cleft lip" is determined, the absence thumb on the legs, defects internal organs, their anomalous development. Only a few survive and remain mentally retarded throughout their lives.
• polyploidy(multiple number of chromosomes). Patau syndrome is manifested by external and mental anomalies. Children are born deaf and mentally retarded. The chromosome theory of heredity is always confirmed, which makes it possible to predict the development of the fetus even in the womb and, if necessary, terminate the pregnancy.