The section of the chromosome in which the gene is located is called. What is the name of the chromosome section in which the gene is located - patterns of inheritance

"chromosome" - words that are familiar to every student. But the idea of ​​this issue is quite generalized, since delving into the biochemical jungle requires special knowledge and a desire to understand all this. And if it is present at the level of curiosity, then it quickly disappears under the weight of the presentation of the material. Let's try to understand the intricacies in a scientific polar form.

A gene is the smallest structural and functional piece of information about heredity in living organisms. In fact, it is a small piece of DNA that contains knowledge about a specific sequence of amino acids for building a protein or functional RNA (from which a protein will also be synthesized). The gene determines those traits that will be inherited and transmitted by descendants further along the genealogical chain. In some unicellular organisms, there is a gene transfer that has nothing to do with the reproduction of their own kind, it is called horizontal.

Genes bear a huge responsibility for how each cell and the organism as a whole will look and work. They rule our life from the moment of conception to the very last breath.

The first scientific step forward in the study of heredity was made by the Austrian monk Gregor Mendel, who in 1866 published his observations on the results of crossing peas. The hereditary material that he used clearly showed the patterns of transmission of traits, such as the color and shape of the peas, as well as flowers. This monk formulated the laws that formed the beginning of genetics as a science. Genes are inherited because parents give their child half of all their chromosomes. Thus, the traits of mom and dad, mixing, form a new combination of existing traits. Fortunately, there are more options than living beings on the planet, and it is impossible to find two absolutely identical creatures.

Mendel showed that hereditary inclinations do not mix, but are transmitted from parents to descendants in the form of discrete (separate) units. These units, represented in individuals by pairs (alleles), remain discrete and are transmitted to the next generations in male and female ha-metas, each of which contains one unit from each pair. In 1909, Danish botanist Johansen named these units genes. In 1912, a geneticist from the United States of America, Morgan, showed that they are found on chromosomes.

More than a century and a half have passed since then, and research has advanced further than Mendel could have imagined. At the moment, scientists have settled on the opinion that the information in the genes determines the growth, development and functions of living organisms. And maybe even their death.

Classification

The structure of a gene contains not only information about a protein, but also instructions when and how to read it, as well as empty areas necessary to separate information about different proteins and stop the synthesis of an information molecule.

There are two forms of genes:

1. Structural - they contain information about the structure of proteins or RNA chains. The sequence of nucleotides corresponds to the arrangement of amino acids.
2. Functional genes are responsible for the correct structure of all other DNA regions, for the synchronicity and sequence of its reading.

Today scientists can answer the question: how many genes are there in a chromosome? The answer will surprise you: about three billion pairs. And this is only in one of twenty-three. The genome is called the smallest structural unit, but it can change a person's life.

Mutations

Accidental or deliberate change in the sequence of nucleotides included in the DNA chain is called a mutation. It can practically not affect the structure of the protein, but can completely distort its properties. This means that there will be local or global consequences of such a change.

By themselves, mutations can be pathogenic, that is, manifest as diseases, or lethal, preventing the body from developing to a viable state. But most of the changes are imperceptible to humans. Deletions and duplications are constantly occurring within the DNA, but do not affect the life course of each individual.

Deletion is the loss of a portion of a chromosome that contains certain information. Sometimes these changes are beneficial for the body. They help him defend himself against external aggression, such as the human immunodeficiency virus and the plague bacteria.

Duplication is a duplication of a section of a chromosome, which means that the set of genes that it contains also doubles. Due to the repetition of information, it is less susceptible to selection, which means that it can accumulate mutations and change the body faster.

Gene properties

Each person has a huge Genes - these are functional units in its structure. But even such small areas have their own unique properties that allow maintaining the stability of organic life:

1. Discreteness is the ability of genes not to mix.
2. Stability - preservation of structure and properties.
3. Lability is the ability to change under the influence of circumstances, to adapt to hostile conditions.
4. Multiple allelism is the existence of genes within DNA that, encoding the same protein, have a different structure.
5. Allelicity is the presence of two forms of one gene.
6. Specificity - one trait = one inherited gene.
7. Pleiotropy is the multiplicity of effects of one gene.
8. Expressiveness - the degree of expression of a trait that is encoded by a given gene.
9. Penetrance is the frequency of occurrence of a gene in a genotype.
10. Amplification is the appearance of a significant number of copies of a gene in DNA.

Genome

The human genome is all hereditary material that is found in a single human cell. It is it that contains instructions on the construction of the body, the work of organs, physiological changes. The second definition of this term reflects the structure of the concept, not the function. The human genome is a collection of genetic material packed in a haploid set of chromosomes (23 pairs) and belonging to a specific species.

The backbone of the genome is a molecule well known as DNA. All genomes contain at least two types of information: encoded information about the structure of intermediary molecules (the so-called RNA) and protein (this information is contained in genes), as well as instructions that determine the time and place of this information during the development of the organism. Genes themselves occupy a small part of the genome, but at the same time are its basis. The information stored in the genes is a kind of instruction for making proteins, the main building blocks of our body.

However, for a complete characterization of the genome, the information on the structure of proteins contained in it is insufficient. We also need data on the elements that take part in the work of genes, regulate their manifestation at different stages of development and in different life situations.

But even this is not enough for a complete definition of the genome. After all, it also contains elements that contribute to its self-reproduction (replication), compact packing of DNA in the nucleus and some other still incomprehensible areas, sometimes called “selfish” (that is, as if serving only for themselves). For all these reasons, at the moment, when it comes to the genome, they usually mean the entire set of DNA sequences presented in the chromosomes of the cell nuclei of a certain type of organism, including, of course, genes.

Genome size and structure

It is logical to assume that the gene, genome, chromosome differ in different representatives of life on Earth. They can be both infinitely small and huge and contain billions of gene pairs. The structure of a gene will also depend on whose genome you are examining.

According to the ratio between the size of the genome and the number of genes included in it, two classes can be distinguished:

1. Compact genomes with no more than ten million bases. Their set of genes is strictly correlated with size. Most typical for viruses and prokaryotes.
2. Large genomes are composed of more than 100 million base pairs with no relationship between their length and the number of genes. More common in eukaryotes. Most of the nucleotide sequences in this class do not encode proteins or RNA.

Studies have shown that there are about 28 thousand genes in the human genome. They are unevenly distributed across chromosomes, but the meaning of this trait remains a mystery to scientists.

Chromosomes

Chromosomes are a way of packaging genetic material. They are found in the nucleus of every eukaryotic cell and are made up of one very long DNA molecule. They can be easily seen under a light microscope during fission. A karyotype is a complete set of chromosomes that is specific to each individual species. Mandatory elements for them are the centromere, telomeres and points of replication.

Chromosome changes during cell division

Chromosomes are successive links in the information transmission chain, where each next includes the previous one. But they also undergo certain changes in the process of cell life. So, for example, in the interphase (the period between divisions), the chromosomes in the nucleus are loosely located, take up a lot of space.

When the cell prepares for mitosis (i.e., the process of splitting in two), chromatin thickens and coils into chromosomes, and now it becomes visible through a light microscope. In metaphase, chromosomes resemble rods, close to each other and connected by a primary constriction, or centromere. It is she who is responsible for the formation of the division spindle, when groups of chromosomes line up. Depending on the location of the centromere, there is such a classification of chromosomes:

1. Acrocentric - in this case, the centromere is located polarly with respect to the center of the chromosome.
2. Submetacentric, when the arms (that is, the areas before and after the centromere) are of unequal length.
3. Metacentric if the centromere separates the chromosome exactly in the middle.

This classification of chromosomes was proposed in 1912 and is used by biologists up to the present day.

Chromosome abnormalities

As with other morphological elements of a living organism, structural changes can also occur with chromosomes that affect their functions:

1. Aneuploidy. This is a change in the total number of chromosomes in a karyotype due to the addition or removal of one of them. The consequences of such a mutation can be fatal for the unborn fetus, as well as lead to birth defects.
2. Polyploidy. It manifests itself in the form of an increase in the number of chromosomes, a multiple of half of their number. It is most commonly found in plants such as algae and fungi.
3. Chromosomal aberrations, or rearrangements, are changes in the structure of chromosomes under the influence of environmental factors.

Genetics

Genetics is a science that studies the patterns of heredity and variability, as well as the biological mechanisms that provide them. Unlike many other biological sciences, it has strived to be an exact science since its inception. The whole history of genetics is the history of the creation and use of more and more precise methods and approaches. Ideas and methods of genetics play an important role in medicine, agriculture, genetic engineering, microbiological industry.

Heredity is the ability of an organism to provide a number of morphological, biochemical and physiological signs and characteristics. In the process of inheritance, the main species-specific, group (ethnic, population) and family features of the structure and functioning of organisms, their ontogenesis (individual development) are reproduced. Not only certain structural and functional characteristics of the organism are inherited (facial features, some features of metabolic processes, temperament, etc.), but also the physicochemical features of the structure and functioning of the main biopolymers of the cell. Variability is a variety of traits among representatives of a certain species, as well as the property of offspring to acquire differences from parental forms. Variability together with heredity are two inseparable properties of living organisms.

Down Syndrome

Down syndrome is a genetic disease in which the karyotype consists of 47 chromosomes in humans instead of the usual 46. This is one of the forms of aneuploidy mentioned above. In the twenty-first pair of chromosomes, an additional one appears, which brings extra genetic information into the human genome.

The syndrome got its name in honor of the doctor, Don Down, who discovered and described it in the literature as a form of mental disorder in 1866. But the genetic background was discovered almost a hundred years later.

Epidemiology

At the moment, the karyotype of 47 chromosomes in humans occurs once per thousand newborns (previously, the statistics were different). This became possible due to the early diagnosis of this pathology. The disease is independent of the mother's race, ethnicity, or social status. Age influences. The chances of giving birth to a child with Down syndrome increase after thirty-five years, and after forty, the ratio of healthy children to sick children is already 20 to 1. A father's age over forty also increases the chances of having a child with aneuploidy.

Down syndrome forms

The most common variant is the appearance of an additional chromosome in the twenty-first pair through a non-hereditary path. It is due to the fact that during meiosis, this pair does not diverge along the fission spindle. In five percent of patients, mosaicism is observed (an additional chromosome is not found in all cells of the body). Together they make up ninety-five percent of the total number of people with this congenital pathology. In the remaining five percent of cases, the syndrome is caused by a hereditary trisomy of the twenty-first chromosome. However, the birth of two children with this disease in the same family is negligible.

Clinic

A person with Down syndrome can be recognized by their characteristic external signs, here are some of them:

Flattened face;
- a shortened skull (the transverse dimension is greater than the longitudinal one);
- skin fold on the neck;
- a fold of skin that covers the inner corner of the eye;
- excessive joint mobility;
- decreased muscle tone;
- flattening of the occiput;
- short limbs and fingers;
- the development of cataracts in children over eight years old;
- anomalies in the development of teeth and hard palate;
- congenital heart defects;
- the presence of an epileptic syndrome is possible;
- leukemia.

But, of course, it is impossible to make a diagnosis based only on external manifestations. It is necessary to carry out karyotyping.

Conclusion

Gene, genome, chromosome - it seems that these are just words, the meaning of which we understand in a generalized and very distant manner. But in fact, they strongly influence our life and, by changing, make us change too. A person knows how to adapt to circumstances, whatever they may be, and even for people with genetic abnormalities there will always be a time and place where they will be irreplaceable.

Genetics(from the Greek "genesis" - origin) - the science of the laws of heredity and variability of organisms.
Gene(from the Greek. "genos" - birth) is a part of the DNA molecule, which is responsible for one feature, that is, for the structure of a certain protein molecule.
Alternative signs - mutually exclusive, contrasting signs (color of pea seeds is yellow and green).
Homologous chromosomes(from the Greek "homos" - the same) - paired chromosomes, the same shape, size, set of genes. In a diploid cell, the set of chromosomes is always paired:
one chromosome from a pair of maternal origin, the other from paternal origin.
Locus - the part of the chromosome in which the gene is located.
Allelic genes - genes located at the same loci of homologous chromosomes. The development of alternative traits (dominant and recessive - yellow and green color of pea seeds) is controlled.
Genotype - a set of hereditary characteristics of an organism, received from parents, is a hereditary development program.
Phenotype - a set of signs and properties of an organism, manifested in the interaction of the genotype with the environment.
Zygote(from the Greek. "zygote" - paired) - a cell formed by the fusion of two gametes (sex cells) - female (egg) and male (sperm). Contains a diploid (double) set of chromosomes.
Homozygote(from the Greek "homos" - the same and zygote) a zygote having the same alleles of a given gene (both dominant AA or both recessive aa). A homozygous individual in the offspring does not split.
Heterozygote(from the Greek "heteros" - another and a zygote) - a zygote that has two different alleles for a given gene (Aa, Bb). A heterozygous individual in the offspring gives a splitting according to this trait.
Dominant feature(from Lat. "edominas" - dominant) - the predominant trait, manifested in the offspring of
heterozygous individuals.
Recessive trait(from Lat. "recessus" - a retreat) a trait that is inherited, but suppressed, without manifesting itself in heterozygous offspring obtained by crossing.
Gamete(from the Greek "gametes" - spouse) - the reproductive cell of a plant or animal organism, carrying one gene from an allelic pair. Gametes always carry genes in a "pure" form, as they are formed by meiotic cell division and contain one of a pair of homologous chromosomes.
Cytoplasmic inheritance- extra-nuclear heredity, which is carried out with the help of DNA molecules located in plastids and mitochondria.
Modification(from Lat. "modification" - modification) - a non-hereditary change in the phenotype that occurs under the influence of environmental factors within the normal reaction of the genotype.
Modification variability - variability of the phenotype. The response of a specific genotype to different environmental conditions.
Variational series- a series of modification variability of the trait, which is composed of individual values ​​of modifications, arranged in the order of increasing or decreasing the quantitative expression of the trait (leaf size, number of flowers in an ear, change in wool color).
Variation curve- a graphic expression of the variability of a trait, reflecting both the range of variation and the frequency of occurrence of individual variants.
Reaction rate - the limit of modification variability of the trait, due to the genotype. Plastic signs have a wide reaction rate, non-plastic ones - a narrow one.
Mutation(from Lat. "mutatio" - change, change) - hereditary change in the genotype. Mutations are: gene, chromosomal, generative (in gametes), extra-nuclear (cytoplasmic), etc.
Mutagenic factor - the factor causing the mutation. There are natural (natural) and artificial (human-induced) mutagenic factors.
Monohybrid crossing- crossing of forms that differ from each other in one pair of alternative characters.
Dihybrid crossing-crossing forms that differ from each other in two pairs of alternative features.
Analyzing cross- crossing the test organism with another, which is a recessive homozygote for this trait, which makes it possible to establish the genotype of the test subject. It is used in plant and animal breeding.
Chained inheritance- joint inheritance of genes localized on the same chromosome; genes form linkage groups.
Crossingsr (cross) - mutual exchange of homologous regions of homologous chromosomes during their conjugation (in prophase I of meiosis I), leading to a rearrangement of the original combinations of genes.
Gender of organisms - a set of morphological and physiological characteristics that are determined at the time of fertilization by the sperm of the egg and depend on the sex chromosomes carried by the sperm.
Sex chromosomes - chromosomes in which the male sex differs from the female. The sex chromosomes of the female body are all the same (XX) and determine the female gender. The sex chromosomes of the male body are different (XY): X defines female
floor, Y- male. Since all spermatozoa are formed by meiotic cell division, half of them carry X chromosomes, and half carry Y chromosomes. The likelihood of getting male and female is the same,
Population genetics - a branch of genetics that studies the genotypic composition of populations. This makes it possible to calculate the frequency of mutant genes, the probability of their occurrence in a homo- and heterozygous state, as well as to monitor the accumulation of harmful and useful mutations in populations. Mutations serve as material for natural and artificial selection. This section of genetics was founded by S.S.Chetverikov and was further developed in the works of N.P. Dubinin.

Genetics

Gene

Allelic genes

Allele- each gene of an allelic pair.

Alternative signs

Dominant feature

Recessive trait

Homozygote

Heterozygote

Genotype

Phenotype

Hybridological method

Monohybrid crossing

Dihybrid crossing

Polyhybrid crossing

Genetics- a science that studies the laws of heredity and variability.

Gene Is a section of a DNA molecule that contains information about the primary structure of one protein.

Allelic genes Is a pair of genes that determine the contrasting characteristics of an organism.

Allele- each gene of an allelic pair.

Alternative signs- these are mutually exclusive, contrasting signs (yellow - green; high - low).

Dominant feature(predominant) is a trait that appears in first-generation hybrids when crossing representatives of pure lines. (A)

Recessive trait(suppressed) is a trait that does not appear in first generation hybrids when crossing representatives of pure lines. (a)

Homozygote- a cell or organism containing the same alleles of the same gene (AA or aa).

Heterozygote- a cell or organism containing different alleles of the same gene (Aa).

Genotype- the set of all genes of the body.

Phenotype- a set of characteristics of organisms that are formed when the genotype interacts with the environment.

Hybridological method- a method that involves the study of the characteristics of parental forms, manifested in a number of generations in offspring obtained by hybridization (crossing).

Monohybrid crossing- this is the crossing of forms that differ from each other in one pair of studied contrasting characters, which are inherited.

Dihybrid crossing- This is a crossing of forms that differ from each other in two pairs of contrasting traits studied, which are inherited.

Polyhybrid crossing- This is the crossing of forms that differ from each other in several pairs of contrasting traits under study, which are inherited.

Eukaryotic chromosomes are DNA-containing structures in the nucleus, mitochondria, and plastids. Genes on the same chromosome form a linkage group and are inherited together. Genes are located linearly on chromosomes. The region of the chromosome where a particular gene is located is called a locus. Gametes always carry genes in a "pure" form, as they are formed by meiotic cell division and contain one of a pair of homologous chromosomes.

This makes it possible to calculate the frequency of mutant genes, the probability of their occurrence in a homo- and heterozygous state, as well as to monitor the accumulation of harmful and useful mutations in populations. This section of genetics was founded by S.S.Chetverikov and was further developed in the works of N.P. Dubinin. DNA. The ability to dissect and splicate a DNA molecule made it possible to create a hybrid bacterial cell with human genes responsible for the synthesis of the hormone insulin and interferon.

The analysis of genotype elements (linkage groups, genes and intragenic structures) is carried out, as a rule, by phenotype (indirectly by traits). Depending on the tasks and characteristics of the object under study, genetic analysis is carried out at the population, organismic, cellular and molecular levels. In case of incomplete dominance, the genotype and phenotype splitting coincides 1: 2: 1. Studying monohybrid crossing, G. Mendel developed different types of crossing, including analyzing one.

Mendel showed that the law of uniformity of the first generation hybrids is valid for any number of traits, including the dihybrid crossing. Vector is a DNA molecule capable of incorporating foreign DNA and autonomous replication, serving as a tool for introducing genetic information into a cell.

II. Learning new material.

The genetic code is the correspondence between triplets in DNA (or RNA) and the amino acids of proteins. Gene therapy is the introduction of genetic material (DNA or RNA) into a cell to restore normal function. Genome - General genetic information contained in the genes of an organism, or the genetic makeup of a cell. Reporter gene - a gene whose product is determined using simple and sensitive methods and whose activity is normally absent in the tested cells.

Dominance is the predominant manifestation of only one allele in the formation of a trait in a heterozygous cell. Interferons are proteins synthesized by vertebrate cells in response to a viral infection and suppressing their development. Cloning of cells - their separation by sieving in a nutrient medium and obtaining colonies containing offspring from an isolated cell.

A prophage is an intracellular state of a phage under conditions when its lytic functions are suppressed. Processing is a special case of modification (see modification), when the number of units in the biopolymer decreases. Pleiotropia is a phenomenon of multiple gene actions. It is expressed in the ability of one gene to influence several phenotypic traits.

Initially, the term was proposed to refer to structures found in eukaryotic cells, but in recent decades, they increasingly speak of bacterial or viral chromosomes. In 1902 T. Boveri and in 1902-1903 W. Setton (Walter Sutton) independently put forward a hypothesis about the genetic role of chromosomes.

In 1933, T. Morgan received the Nobel Prize in Physiology or Medicine for the discovery of the role of chromosomes in heredity. In the course of the cell cycle, the appearance of the chromosome changes. In the interphase, these are very delicate structures that occupy separate chromosomal territories in the nucleus, but are not noticeable as separate formations during visual observation. In mitosis, chromosomes are converted into densely packed elements that can resist external influences, maintain their integrity and shape.

Mitotic chromosomes can be seen in any organism whose cells are able to divide by mitosis, with the exception of the yeast S. cerevisiae, whose chromosomes are too small. At the metaphase stage of mitosis, chromosomes consist of two longitudinal copies, called sister chromatids, and which are formed during replication. In metaphase chromosomes, sister chromatids are connected in the region of the primary constriction called the centromere.

The centromere assembles the kinetochore, a complex protein structure that determines the attachment of the chromosome to the microtubules of the fission spindle - the movers of the chromosome in mitosis. The centromere divides the chromosomes into two parts called the shoulders. In most species, the short arm of the chromosome is denoted by the letter p, and the long arm by the letter q. Chromosome length and centromere position are the main morphological features of metaphase chromosomes.

In addition to the above three types, S.G. Navashin also distinguished telocentric chromosomes, that is, chromosomes with only one arm. However, according to modern concepts, there are no truly telocentric chromosomes. The second shoulder, even if it is very short and invisible in an ordinary microscope, is always present. An additional morphological feature of some chromosomes is the so-called secondary constriction, which outwardly differs from the primary one in the absence of a noticeable angle between the segments of the chromosome.

This classification of chromosomes based on the ratio of shoulder lengths was proposed in 1912 by the Russian botanist and cytologist S.G. Navashin. In many birds and reptiles, the chromosomes in the karyotype form two distinct groups: macrochromosomes and microchromosomes. These chromosomes are extremely transcriptionally active and are observed in growing oocytes when the processes of RNA synthesis leading to yolk formation are most intense. Typically, mitotic chromosomes are several microns in size.

In the cells of each organism there is a certain number of chromosomes. There are a lot of genes in them. A person has 23 pairs (46) chromosomes, about 100,000 genes. Genes are located in chromosomes. Many genes are localized on one chromosome. A chromosome with all genes in it forms a linkage group. The number of linkage groups is equal to the haploid set of chromosomes. A person has 23 clutch groups. Genes located on the same chromosome are not absolutely linked. During meiosis, when chromosomes are conjugated, homologous chromosomes exchange parts. This phenomenon is called crossing over and can occur anywhere on the chromosome. The farther the loci on the same chromosome are located from each other, the more often regions can be exchanged between them (Fig. 76). In the Drosophila fly, the genes for wing length (V - long and v - short) and body color (B - gray and b - black) are in the same pair of homologous chromosomes, i.e. belong to the same clutch group. If a fly with a gray body color and long wings is crossed with a black fly with short wings, then in the first generation all flies will have a gray body color and long wings (Fig. 77). As a result of crossing a diheterozygous male with a homozygous recessive female fly will be like their parents. This is because genes on the same chromosome are inherited linked. In the male Drosophila fly, the grip is complete. If you cross a diheterozygous female with a homozygous recessive male, then some of the flies will look like their parents, and in Rice. 76. Crossing over. 1 - two homologous chromosomes; 2 — their crossover during conjugation; 3 - two new combinations of chromosomes. The other part will be a recombination of characters. Such inheritance takes place for genes of the same linkage group, between which crossing over can occur. This is an example of incomplete gene linkage. The main provisions of the chromosomal theory of heredity... Genes are located on chromosomes. Genes on a chromosome are arranged in a linear fashion. Rice. 77. Linked inheritance of genes for body color and wing condition in the fruit fly. The gray gene (B) dominates the black body gene (b), the long wing gene (V) dominates the short wing gene (v). B and V are on the same chromosome. A - complete linkage of genes due to the absence of chromosome crossing in Drosophila males: PP - gray female with long wings (BBVV) crossed with a black short-winged male (bbvv); F1 - gray male with long wings (BbVv) crossed with a black short-winged female (bbvv); F2 - since the male does not cross-over, two types of offspring will appear: 50% - black short-winged and 50% - gray ones with normal wings; b - incomplete (partial) linkage of characters due to the crossing of chromosomes in Drosophila females: PP - female with long wings (BBVV) crossed with a black short-winged male (bbvv); F1 - gray female with long wings (BbVv) crossed with a black short-winged male (bbvv). F2 - since the female has a crossing over of homologous chromosomes, four types of gametes are formed and four species of offspring will appear: necrossovers - gray with long wings (BbVv) and black short-winged (bbvv), crossovers - black with long wings (bbVv), gray short-winged (Bbvv ). ... Each gene occupies a specific place - a locus .. Each chromosome is a linkage group. The number of linkage groups is equal to the haploid number of chromosomes. Allelic genes are exchanged between homologous chromosomes. The distance between genes is proportional to the percentage of crossing over between them. Questions for self-control 1. Where are the genes? 2. What is a clutch group? 3. What is the number of clutch groups? 4. How are genes linked on chromosomes? 5. How is the trait of wing length and body color inherited in the Drosophila fly? 6. Offspring with what traits will appear when crossing a homozygous female with long wings and a gray body color with a homozygous black male with short wings? Offspring with what traits will appear when crossing a diheterozygous male with a homozygous recessive female? 8. What kind of gene linkage takes place in the male Drosophila? 9. What offspring will be when a diheterozygous female is crossed with a homozygous recessive male? 10. What is the linkage of genes in the female Drosophila? 11. What are the main provisions of the chromosomal theory of heredity? Key words of the topic "Chromosomal theory of heredity" genes clutch group cell length colocus place of fly heredity exchange coloration organism couples recombination generation position descendants distance resultparents male male crossbreedingtelotheorysection of chromosomescolorparthuman number Chromosomal sex determination mechanism Phenotypic differences between individuals of different sex are due to the genotype. Genes are found on chromosomes. There are rules for individuality, constancy, chromosome pairing. The diploid set of chromosomes is called karyotype. In the female and male karyotype 23 pairs (46) of chromosomes (Fig. 78). 22 pairs of chromosomes are the same. They are called autosomes. 23rd pair of chromosomes - sex chromosomes. In the female karyotype, one Rice. 78. Karyotypes of different organisms. 1 - a person; 2 - a mosquito; 3 plants skerdy.kovye sex chromosomes XX. In the male karyotype, the sex chromosomes are XY. The Y chromosome is very small and contains few genes. The combination of sex chromosomes in the zygote determines the sex of the future organism. When the germ cells mature, as a result of meiosis, the gametes receive a haploid set of chromosomes. Each egg has 22 autosomes + an X chromosome. The sex that forms gametes that are the same on the sex chromosome is called the homogametic sex. Half of the sperm contains 22 autosomes + X chromosome, and half of 22 autosomes + Y. The sex that forms gametes that are different on the sex chromosome is called heterogametic. The sex of the unborn child is determined at the time of fertilization. If an egg is fertilized by a sperm with an X chromosome, a female organism develops, if the Y chromosome is a male one (Fig. 79). Rice. 79. Chromosomal mechanism of sex formation. The probability of having a boy or girl is 1: 1 or 50 \%: 50 \%. This sex determination is typical for humans and mammals. Some insects (grasshoppers and cockroaches) do not have a Y chromosome. Males have one X chromosome (X0), and females have two (XX). In bees, females have a 2n set of chromosomes (32 chromosomes), and males have n (16 chromosomes). Women have two sex X chromosomes in their somatic cells. One of them forms a lump of chromatin, which is noticeable in the interphase nuclei when treated with a reagent. This lump is Barr's little body. Men have no Barr's body because they only have one X chromosome. If during meiosis two XX chromosomes enter the egg at once and such an egg is fertilized by a sperm, then the zygote will have a larger number of chromosomes. For example, an organism with a set of chromosomes XXX (trisomy on the X chromosome) phenotype - girl. She has underdeveloped sex glands. In the nuclei of somatic cells, two Barr bodies are distinguished. An organism with a set of chromosomes XXY (Klinefelter syndrome) the phenotype is a boy. He has underdeveloped testes, physical and mental retardation. There is a Barr body. Chromosomes XO (monosomy on the X chromosome)- define Shereshevsky-Turner syndrome. An organism with such a set is a girl. She has underdeveloped sex glands, short stature. No Barr's body. An organism that does not have an X chromosome, but contains only a Y chromosome is not viable. Inheritance of traits whose genes are located on the X or Y chromosomes is called sex-linked inheritance. If genes are on the sex chromosomes, they are sex-linked. A person has a gene on the X chromosome that determines the characteristic of blood clotting. The recessive gene causes the development of hemophilia. The X chromosome contains a gene (recessive) that is responsible for the manifestation of color blindness. Women have two X chromosomes. A recessive trait (hemophilia, color blindness) appears only if the genes responsible for it are located on two X chromosomes: XhXh; XdXd. If one X chromosome has a dominant gene H or D, and the other has a recessive h or d, then there will be no hemophilia or color blindness. Men have one X chromosome. If it contains the H or h gene, then these genes will certainly manifest their effect, because the Y chromosome does not carry these genes. A woman may be homozygous or heterozygous for genes localized on the X chromosome, but recessive genes appear only in a homozygous state .If genes are on the Y chromosome (Dutch inheritance), then the signs caused by them are transmitted from father to son. For example, hairiness of the ears is inherited through the Y chromosome. Men have one X chromosome. All genes in it, including recessive ones, are manifested in the phenotype. In the heterogametic sex (male), most of the genes localized on the X chromosome are located in hemizygous condition, that is, they do not have an allelic pair. The Y chromosome contains some genes that are homologous to the genes of the X chromosome, for example, genes for hemorrhagic diathesis, general color blindness, etc. These genes are inherited through both the X and the Y chromosome ... Questions for self-control 1. What are the rules of chromosomes? 2. What is a karyotype? 3. How many autosomes does a person have? 4. What chromosomes in humans are responsible for the development of sex? 5. What is the likelihood of having a boy or girl? 6. How is gender determined in grasshoppers and cockroaches? 7. How is the sex of bees determined? 8. How is sex determined in butterflies and birds? 9. What is Barr's body? 10. How can you determine the presence of a Barr body? 11. How can you explain the appearance of more or less chromosomes in a karyotype? 12. What is sex-linked inheritance? 13. What genes in humans are inherited sex-linked? 14. How and why do sex-linked recessive genes in women manifest their effect? ​​15. How and why do recessive genes linked to the X chromosome in men manifest their effect? 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