Presentation - sex determination and inheritance of sex-linked characteristics. Presentation for the lesson "Genetics of Sex"

Adrenogenital syndrome. Violation of hormone production. Dual structure of the genital organs. In most animals, sex is determined genetically. Hermaphroditism is the presence of both types of gonads in an individual. In humans, clothing, makeup, perfume, etc. play an important role. Mechanisms for determining gender. Examples of determining gender by environmental factors. Examples of false hermaphroditism (pseudohermaphroditism). Reproduction is the ability of living organisms to reproduce their own kind.

"PCR" - DNA sequence. Kary Mullis. Elongation. Components of the reaction. Stages of PCR research. Detection of amplification products. Amplification. Some types of PCR. Detection. Real-time PCR. Advantages of the PCR method. Use of intercalating agents. Scheme of doubling DNA fragments. Annealing. Process. Molecular genetic diagnostic methods. Stage. Melting curves. Disadvantages of the PCR method.

"Genetic epidemiology" - A number of researchers. Efficiency. Classification of populations. Archaeologists. Today's ethnic groups of the Caucasus. Aul. Isolates. Genetic epidemiology in human populations. Human isolates. Dagestan isolates. Small populations. Modern big cities. Problems and prospects. Search for isolates.

"Applied genetics" - Nitrogen fixation. Methods for obtaining transgenic animals. Each of the 100 trillion human cells has a nucleus containing 46 chromosomes. "Who will be the first to shout hurray?" Genetic engineering of bacteria. Is it possible to interfere with nature? Transgenic organisms are genetically rearranged using genetic engineering methods. 1-2% of experimental embryos turned into adult frogs. The resulting animals are CHIMERAS (contain different types of cells).

“Methods of genetic analysis” - Human and guppy karyotypes. Mendel's laws. Genetic problems. Second generation analysis. Sign. Basics of genetic analysis. Number of types formed. Genetic analysis algorithm. Kirpichnikov Valentin Sergeevich. Basic principle of genetic analysis. The number of types and combinations of gametes formed. Experimental work. It is necessary to select parents who are homozygous for the characteristics being studied. Karyotype.

"Chromosomes" - Inversions. Each chromosome contains hereditary instructions. Chromatid. Karyotype. Chromosome layout. Chromosomes like lamp brushes. Giant chromosomes. Types of chromosomes. Structure and functions of chromosomes. Polytene chromoosmata. Meaning of deletion. All human chromosomes. Chromosome structure disorders. Diploid set of chromosomes. The meaning of the centromere. Loss of internal area. Chromosome. Giant chromosomes from salivary gland cells.

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Gender Gender is a set of characteristics and properties of an organism that determine its participation in reproduction.

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The sex of an individual can be determined: a) before fertilization of the egg by the sperm (programmatic sex determination); b) at the moment of fertilization (syngamous sex determination); c) after fertilization (epigamous sex determination).

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. Sex chromosomes are usually referred to as X- and Y-chromosomes. Depending on their combination in organisms, 5 types of chromosomal sex determination are distinguished: 1) XX, XO (O denotes the absence of chromosomes) occurs in Protenor species (insects); 2) XX, XY - it is characteristic, for example, of Drosophila, mammals (including humans); 3) XY, XX - this type of sex determination is typical for butterflies, birds, and reptiles; 4) XO, XX - observed in aphids; 5) haplo-diploid type (2n, n) is found, for example, in bees: males develop from unfertilized haploid eggs, females from fertilized diploid eggs.

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The specific mechanisms linking the development of male or female sex with a certain combination of sex chromosomes varies from organism to organism. In humans, for example, gender is determined by the presence of the Y chromosome: it contains the TDP gene, it encodes the testicle - the determining factor that determines the development of the male sex.

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If the ratio of the number of X chromosomes to the number of sets of autosomes is 0.5, then a male develops, and if it is 1, then a female develops. Human chromosome set

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Inheritance and sex In the sex chromosomes, in addition to the genes that determine the development of sex, “ordinary” phenotypic genes are localized. The peculiarities of their inheritance are determined by the fact that they constitute a heterosome linkage group. The phenomenon of sex-linked inheritance was discovered by T. H. Morgan, who discovered that the inheritance of eye color in Drosophila is related to the sex of the parents - the results of direct and backcrossing were not the same. After conducting a series of experiments, the scientist came to the conclusion that the male Y-chromosome does not contain the region encoding eye color.

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In humans, sex-linked anomalies include color blindness and hemophilia. Since the recessive genes for these diseases are localized on the X chromosomes, men are more likely to suffer from them; women are usually heterozygous and for this reason do not get sick. If a gene is localized on the Y chromosome and there is no homologous allele in the cell, such an organism is called a hemizygote. Some genes may not be located on sex chromosomes, but their manifestation will depend on the sex of the individual: in one sex the trait will appear, in the other it will not. Such traits are called sex-limited traits. These include, for example, the presence of antlers on deer. Typically, the manifestation of a sex-limited trait depends on the hormonal status of the body, primarily on the ratio of sex hormones.

Characterize the mechanism of sex determination and the characteristics of the inheritance of sex-linked traits;

Learn to solve problems on the inheritance of sex-linked traits

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1. Gender determination

As is known, most animals and dioecious plants are dioecious organisms, and within a species the number of male individuals is approximately equal to the number of female individuals.

The inheritance of an organism's characteristics is usually determined by genes. The mechanism of sex determination has a different character - chromosomal.

Sex is most often determined at the time of fertilization.

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Chromosomes that are the same in both sexes are called autosomes.

Chromosomes on which the chromosome sets of male and female organisms differ are called sex chromosomes.

In humans, the female sex is homogametic, that is, all eggs carry the X chromosome.

The male body is heterogametic, that is, it forms two types of gametes - 50% of gametes carry the X chromosome and 50% carry the Y chromosome.

1. Gender determination

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If a zygote carrying two X chromosomes is formed during fertilization, then a female organism will be formed from it, if an X chromosome and a Y chromosome will form a male organism.

Since the female body has two identical sex chromosomes, it can be considered as homogametic, male, forming two types of gametes - as heterogametic.

1. Gender determination

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The sex of Drosophila is also determined, which has 3 pairs of autosomes and one pair of sex chromosomes. The female sex is homogametic, sex chromosomes are XX; male – heterogametic, sex chromosomes XY.

Sex, like in humans, is determined at the moment of fusion of gametes.

1. Gender determination

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In Drosophila, red eye color is dominant over white. When red-eyed females were crossed with white-eyed males, in the first generation all the offspring turned out to be red-eyed.

If you cross F1 hybrids with each other, then in the second generation all females turn out to be red-eyed, and in males a split occurs - 50% white-eyed and 50% red-eyed.

1. Gender determination

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If you cross white-eyed females and red-eyed males with each other (reciprocal crossing), then in the first generation all the females turn out to be red-eyed, and the males are white-eyed.

In F2, half of the females and males are red-eyed, half are white-eyed.

T. Morgan was able to explain the results of the observed split in eye color only by assuming that the gene responsible for eye color is localized on the X chromosome, and the Y chromosome does not contain such genes.

Thus, thanks to the crosses carried out, a very important conclusion was made: the eye color gene is sex-linked, that is, it is located on the X chromosome.

1. Gender determination

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1. Gender determination

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So, in Drosophila and humans, the female sex is homogametic, and the general pattern of sex inheritance in these two species is the same. In some species of living beings, chromosomal sex determination is completely different.

In some insects (grasshoppers), males have only one sex chromosome (XO) in their chromosome set, and females are homogametic (XX).

In butterflies, birds and reptiles, males are homogametic (XX), and females are heterogametic (XY).

1. Gender determination

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Bees and ants do not have sex chromosomes, and females have a diploid set of chromosomes in their body cells, and males, which develop parthenogenetically (from unfertilized eggs), have a haploid set of chromosomes.

No sex chromosomes have been found in crocodiles. The sex of the embryo developing in the egg depends on the ambient temperature: at high temperatures, more females develop, and if it is cool, more males.

1. Gender determination

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1. Gender determination

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Autosomes:

Chromosomes are the same in males and females.

Sex chromosomes:

Chromosomes that determine the sex of an organism.

Homogametic sex:

If all sex cells carry the same sex chromosome, the sex is homogametic.

Which organisms have male heterogamety according to the XY type:

In most mammals, in Diptera.

Which organisms have male heterogamety of type X0?

In kangaroos, grasshoppers.

Which organisms have female heterogamety of the XY type?

In birds, reptiles, many butterflies.

Which organisms have female heterogamety of type X0?

At what point is the sex of the future organism determined?

At the moment of fusion of gametes.

Let's summarize:

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In humans, a male receives the X chromosome from his mother. Human sex chromosomes have small homologous regions that carry the same genes (for example, the gene for general color blindness); these are conjugation sites.

But most of the genes linked to the X chromosome are absent on the Y chromosome, so these genes (even recessive ones) will manifest themselves phenotypically, since they are represented in the singular in the genotype. Such genes are called hemizygous - one gene per zygote.

For example, genes responsible for blood clotting, for distinguishing colors, a gene responsible for hypertrichosis - in men, increased hairiness of the auricle.

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The human X chromosome contains a number of genes, the recessive alleles of which determine the development of severe anomalies (hemophilia, color blindness).

These anomalies are more common in men (since they are hemizygous for these genes), although the carrier of these anomalies is more often a woman.

In most organisms, only the X chromosome is genetically active, while the Y chromosome is practically inert, since it does not contain genes that determine the characteristics of the organism. In humans, only some genes that are not vital are localized on the Y chromosome (for example, hypertrichosis - increased hairiness of the auricle).

2. Inheritance of sex-linked traits

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Genes located on the Y chromosome are inherited in a special way - only from father to son. The mother passes on only the X chromosome to both son and daughter.

From whom can a son inherit color blindness?

From mother.

Hemophilia?

From mother.

Hypertrichosis?

2. Inheritance of sex-linked traits

What hemizygous genes are shown in the figure?

Genes for hemophilia, color blindness, hypertrichosis.

What genes are called hemizygous?

Genes found in one copy in a zygote.

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The mother is a carrier of the hemophilia gene, the father is healthy. Hemophilia can be:

2. Inheritance of sex-linked traits

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One of the X chromosomes in female mammals is from the father, and the other is from the mother. In 1961, Mary Lyon and Lian Russell independently proposed that the inactivation of one of the X chromosomes in somatic cells occurs randomly. In calico cats, according to Lyon's hypothesis, black and red spots appear due to the fact that different X chromosomes are inactivated in the cells of these spots.

2. Inheritance of sex-linked traits

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Black coloring in cats is determined by the B gene allele located on the X chromosome (XB), while red coloring is determined by the b allele (Xb). If alleles B and b - XBXb are found, then the color of the cat’s coat will be tortoiseshell, tricolor. What kind of offspring is expected from a red cat (XbУ) and a black cat (XBXB)?

2. Inheritance of sex-linked traits

All cats are tortoiseshell, cats are black.

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Hemizygous genes:

Genes that are found in one copy per zygote.

What hemizygous genes does a man have:

Genes responsible for light perception, blood clotting, and hypertrichosis.

How are genes located on the X chromosome transmitted in a man?

Only for daughters.

How are genes located on the Y chromosome in a man transmitted?

Only sons.

How are genes located on a woman's X chromosome transmitted?

They can fall into both the daughter's and son's genotype.

From whom can a son inherit hemophilia? Colorblindness?

Only from the mother.

From whom can a daughter inherit hemophilia?

From father (Xh) and from mother (Xh).

What genotypes do the parents have if their daughter is color blind?

Mother's genotype is ХDХd or ХdХd, father's genotype is ХdУ.

Let's summarize:

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A brown-eyed woman with normal vision, whose father had blue eyes and was color blind, marries a blue-eyed man with normal vision.

What kind of offspring can be expected from this couple if it is known that the gene for brown eyes is inherited as an autosomal dominant trait, and the gene for color blindness is recessive and linked to the X chromosome.

2. Inheritance of sex-linked traits

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In humans, classical hemophilia is inherited as an X-linked recessive trait. Albinism is caused by an autosomal recessive gene. One married couple, normal according to these two characteristics, had a son with both anomalies.

What is the probability that the second son in this family will exhibit both anomalies at the same time?

Hypertrichosis is inherited as a trait linked to the Y chromosome, which manifests itself only by the age of 17 years. One form of ichthyosis is inherited as a recessive, X-linked trait. In a family where the woman is normal in both signs, and the husband has only hypertrichosis, a boy was born with signs of ichthyosis.

1. Determine the likelihood of hypertrichosis in this boy.

2. Determine the probability of having children in this family without both anomalies and what gender they will be.

2. Inheritance of sex-linked traits

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When a hen with striped plumage is crossed with a black rooster, all the hens in the offspring are black, and the roosters have striped plumage. The color gene is linked to the X chromosome.

2. Inheritance of sex-linked traits

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When a hen with striped plumage is crossed with a black rooster, the offspring are all black hens, and the roosters are striped. The color gene is linked to the X chromosome.

What are the genotypes of parents and offspring?

What offspring are expected from crossing hybrids with each other?

2. Inheritance of sex-linked traits

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What are the genotypes of parents and offspring?

What offspring are expected from crossing hybrids with each other?

2. Inheritance of sex-linked traits

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When a hen with black plumage is crossed with a striped rooster, all the hens and roosters in the offspring will have striped plumage. It is known that the gene responsible for plumage color is linked to the X chromosome.

What are the genotypes of parents and offspring?

What offspring are expected from crossing hybrids with each other?

2. Inheritance of sex-linked traits

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• Genetics of sex. Sex-linked inheritance.
• Genetics of sex. Sex-linked inheritance.
• Genetics of sex. Sex-linked inheritance.
• Genetics of sex. Sex-linked inheritance.

“We all stand on the shoulders of our ancestors”

Biology teacher MBOU "Levkovskaya Secondary School No. 7

Chernakova Nina Evgenievna

… all happy families are alike, but every unhappy family is unhappy in its own way

L.N. Tolstoy

• Map of human chromosome set

A human karyotype contains 22 pairs of chromosomes, identical in male and female organisms, and one pair of chromosomes, which distinguishes both sexes. Chromosomes that are the same in both sexes are called autosomes. The chromosomes by which male and female sexes differ from each other are sex or heterochromosomes. The sex chromosomes in women are the same, they are called X chromosomes. Men have an X chromosome and one Y chromosome.

Customer:

Sex ratio

In humans, most vertebrates, many

In insects and dioecious plants, the homogametic sex is the female sex (XX), and the heterogametic sex is the male sex (XY).

In birds, butterflies, reptiles, and tailed amphibians, the homogametic sex is the male sex (XX), and the heterogametic sex is the female sex (XY). The sex chromosomes in these species are sometimes designated by the letters W and Z, with males designated by the symbols ZZ and females by WZ.

In Orthoptera (grasshoppers) homogametic

The sex is female (XX), and the monogametic sex is male (XO).

Haploidy is widespread in bees and ants. These organisms do not have sex chromosomes: females are diploid and males are haploid.

In some animals, sex determination depends on external conditions. For example, in the sea worm Bonelia, individuals that remain free-swimming in the larval stage become females, and larvae attached to the body of an adult female become males as a result of the muscularizing effect of a hormone secreted by the female.

Traits inherited with sex chromosomes X and U, got the name interlocked with the floor

Inheritance of diseases linked to X- chromosome

* classic hemophilia

*absence of gonads

*color blindness (color blindness)

*hypoplasia (darkening of teeth)

*hydrocephalus

• Inheritance linked to - chromosome

* hypertrichosis

*webbed

• Detailed map of the human X chromosome

More than 370 diseases associated with

X chromosome.

Since males have one X chromosome, all genes localized on it, even recessive ones, immediately manifest themselves in the phenotype .

• Clinical signs:
• sub- and intradermal bleeding, hemorrhages in large joints, subcutaneous and intermuscular hematomas, hematuria, severe bleeding from injuries. Cause: deficiency of antihemophilic globulin.
• Inheritance type: X - recessive
• Population frequency– 1: 2500 (boys)

Inheritance of hemophilia

X X

X Y

Female carrier

Healthy man

X Y

X Y

X X

Healthy daughter

Bearer daughter

Healthy son

Sick son

Pedigree of the descendants of Queen Victoria of England. It is believed that the hemophilia gene arose as a result of a mutation in Queen Victoria herself or in one of her parents .

Pattern of inheritance of hemophilia

Mother is a carrier of the hemophilia gene ( XHXh ), father is healthy (KhNU).

Females heterozygous for any of the sex-linked traits are phenotypically normal, but half of their gametes carry a recessive gene. Despite the father having a normal gene, sons of carrier mothers have a 50% chance of developing hemophilia.

• In people's minds, any mention of hemophilia is primarily associated with the image of Tsarevich Alexei - the son of the last Russian Emperor Nicholas II.
• Alexey was sick with hemophilia, having received it from his mother, Empress Alexandra Feodorovna, who inherited the disease from her mother Princess Alice, who in turn received it from her mother, Queen Victoria

Hemophilia.

a hereditary disease characterized by a lifelong disorder of the blood clotting mechanism. In 80% of cases this is due to the absence or insufficiency of antihemophilic globulin in the blood plasma. As a result, blood clotting time is prolonged and patients suffer from severe bleeding even after minimal trauma.

Inheritance of hemophilia in the family of Tsar Nikolai Alexandrovich

Nicholas II

Alexandra

Anastasia

• Sex-linked inheritance
• Sex-linked inheritance
• Sex-linked inheritance
• Sex-linked inheritance

Color blindness, partial color blindness, is a type of color vision disorder. This disease was first described in 1794. Color blindness occurs in 8% of men and 0.5% of women.

When one of these elements is lost, partial color blindness occurs - dichromasia.

Using these tables, color perception can be impaired. In table No. 1, people with normal vision see the number 16.

People with acquired visual impairment have difficulty or do not distinguish the number 96 in Table No. 2 at all.

• In humans, the gene for color blindness is recessive and is located on the X chromosome. In what case can a colorblind man have a colorblind son?

Solution

M.colorblind

D. colorblind

• Clinical signs: increase in head volume, expansion of the ventricles of the brain; thinning and divergence of the skull bones, disproportion of the brain and facial parts of the skull, strabismus, mental retardation and developmental delay, movement and coordination disorders, nystagmus, atrophy of the white matter of the brain.
• Inheritance type: X-recessive.
• Population frequency – 1: 2000

PEDIGREE WITH X-LINKED TYPE OF INHERITANCE

• 1. Only boys on their mother’s side are affected.
• 2. The proband’s parents are healthy.
• 3. The sick man does not transmit the disease, but all his daughters are carriers.
• In a marriage of a carrier woman with a sick man, 50% of daughters and 50% of sons are sick.

Traits linked to the y chromosome

at -the chromosome is called genetically inert or genetically empty, since it contains very few genes.

In humans, the Y chromosome contains a number of genes that regulate spermatogenesis, the manifestation of histocompatibility antigens, affecting the size of teeth, etc.

Anomalies associated with Y -chromosome, which are passed on from the father to all sons (scaly skin, webbed fingers, heavy hair growth on the ears).

• Clinical signs: Excessive hair growth on all parts of the body except the palms and soles. Since the Middle Ages, only 50 cases of congenital hypertyrchiosis have been reported. There are no other developmental abnormalities. Local hypertrichosis can occur with metabolic disorders.
• Type of inheritance: AD. Population frequency unknown.

• Hypertrichosis is inherited as a trait linked to the y chromosome.

What is the probability of having children with this anomaly in a family where the father has hypertrichosis?

Functional disorders

Action

gametes

alcohol

Slowing embryo growth

nicotine

mutations

Inhibits the development of nerve cells

Narcotic substances

radiation

x-ray

radioactive

ultraviolet

Sun, ultrasound, fluorography, x-ray examination, computer, cell phone, household appliances (microwave, TV)

cell

mutation

Damaged DNA

• Phenylketonuria(PKU) is a congenital disease caused by a violation of the transition of phenylalanine to tyrosine and leading to mental retardation.
• Clinical picture Neurological and mental disorders Mental retardation Increased excitability in childhood Specific gait Specific posture and sitting position Unusual position of the limbs Stereotypical movements Increased tendon reflexes Seizures Skin changes Dryness Eczema Vomiting in the newborn period Specific mouse body odor.

• 47 chromosomes – extra X chromosome – XX Y
• Seen in young men
• High growth
• Violation of body proportions (long limbs, narrow chest)
• Developmental delay
• Infertility

• Shereshevsky-Turner syndrome (45; X0) is observed in women. It manifests itself in delayed puberty, underdevelopment of the gonads, and infertility.
• Women with Shereshevsky-Turner syndrome are short, their body is disproportionate - the upper part of the body is more developed, the shoulders are wide, the pelvis is narrow - the lower limbs are shortened, the neck is short with folds, the "Mongoloid" shape of the eyes and a number of other signs.

• Down syndrome occurs when the baby's cells have not 46, but 47 chromosomes. Such children are mentally retarded, 50% have heart defects, a weak immune system... In a newborn, the disease can be diagnosed based on the characteristic appearance of the child: a rounded skull, the back of the head is “sloping”, an oblique eye shape, a wide bridge of the nose, an extra eyelid, light spots gray color on the iris, “Gothic” palate, small ears. The mouth is usually half open; the tongue is thick, often protrudes from the mouth, covered with transverse grooves; the hand is wide, the fingers and toes are shortened, the little finger is often curved; sometimes the fingers are fused (partial or complete syndactyly). The palm often shows a complete transverse fold (monkey fold).

• Remember! The health of your future children is in your hands!
• Remember!
• The health of your future children is in your hands!

You have a choice:

stay healthy and live without problems or...

• You have a choice: stay healthy and live without problems or...

Remember that the health of your future children depends on your health.

• In humans, pseudohypertrophic muscular dystrophy ends in death at 10–20 years of age. In some families, the disease is influenced by a sex-linked recessive gene. The disease has been reported only in boys. If affected boys die before childbearing, why does this disease not disappear from the population?

Presentation on the topic: Genetics of sex. Sex-linked inheritance

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Presentation on the topic: Genetics of sex. Sex-linked inheritance

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Map of the human chromosome set The human karyotype contains 22 pairs of chromosomes, identical in male and female organisms, and one pair of chromosomes, in which both sexes differ. Chromosomes that are the same in both sexes are called autosomes. The chromosomes by which male and female sexes differ from each other are sex or heterochromosomes. The sex chromosomes in women are the same, they are called X chromosomes. Men have an X chromosome and one Y chromosome.

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Genetic explanation of the sex ratio in humans As a result of gametogenesis, all egg cells have one X chromosome, and sperm have two types of gametes: half carry an X chromosome, half carry a Y chromosome. The sex of the offspring depends on which sperm fertilizes the egg. If the egg is fertilized by a sperm carrying the X chromosome, the female body develops. If an egg is fertilized by a sperm carrying a Y chromosome, a male organism develops. Females (XX) have one X chromosome from their father and one X chromosome from their mother. A male (XY) receives the X chromosome only from his mother. This determines the peculiarity of inheritance of genes located on the sex chromosomes. In dioecious organisms, the sex ratio is usually 1:1, i.e. males and females are equally common

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Chromosomal sex determination A sex containing two X chromosomes in its cells is called homogametic, and a sex containing both X and Y chromosomes is called heterogametic. In humans, most vertebrates, many insects and dioecious plants, the homogametic sex is the female (XX), and the heterogametic sex is the male (XY). In birds, butterflies, reptiles, and tailed amphibians, the homogametic sex is the male sex (XX), and the heterogametic sex is the female sex (XY). The sex chromosomes in these species are sometimes designated W and Z, with males designated ZZ and females WZ. In Orthoptera (grasshoppers), the female sex is homogametic (XX), and the male sex (XO) is monogametic.

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Chromosomal sex determination Haploidy is widespread in bees and ants. These organisms do not have sex chromosomes: females are diploid and males are haploid. In some animals, sex determination depends on external conditions. For example, in the sea worm Bonelia, individuals that remain free-swimming in the larval stage become females, and larvae attached to the body of an adult female become males as a result of the muscularizing effect of a hormone secreted by the female.

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Sex-linked traits Traits inherited with sex chromosomes X and Y are called sex-linked. The Y chromosome is called genetically inert or genetically empty because it contains very few genes. In humans, the Y chromosome contains a number of genes that regulate spermatogenesis, manifestations of histocompatibility antigens that affect the size of teeth, etc. There are known anomalies linked to the Y chromosome, which are transmitted from the father to all sons (scaly skin, webbed fingers, heavy hair growth on the ears).

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Sex-linked inheritance Color blindness, partial color blindness, a type of color vision disorder. This disease was first described in 1794. Color blindness occurs in 8% of men and 0.5% of women. When one of these elements is lost, partial color blindness occurs - dichromasia. Using these tables, color perception can be impaired. In table No. 1, people with normal vision see the number 16. People with acquired visual impairment have difficulty or do not at all distinguish the number 96 in table No. 2.

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Hemophilia Hemophilia is a sex-linked recessive disease in which the formation of factor VIII, which accelerates blood clotting, is impaired. The gene that determines the synthesis of factor VIII is located in a region of the X chromosome that does not have a homologue, and is represented by two alleles - a dominant normal and a recessive mutant. Bleeding in hemophilia appears from early childhood. Even mild bruises cause extensive hemorrhages - subcutaneous, intramuscular. Cuts, tooth extraction, etc. are accompanied by life-threatening bleeding and can cause death.

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“Royal disease” This pathological mutation in the F8C gene was in the genotype of the heir to the royal throne, Russian Tsar Alexei. Hemophilia A is a severe hereditary disease that affects almost exclusively males. On average, one out of 10,000 boys is born with this pathology, and only in 70% of cases can one find indications of hereditary transmission of the mutant gene in his pedigree. This means that for every third family in which such a misfortune happened, the latter is a complete surprise.

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Pedigree of inheritance of hemophilia among the Teleuts of the Kemerovo region. In the Kemerovo region, in the Belovsky district, there lives an indigenous population - Teleuts, who have hemophilia. Hemophilia can be traced back five generations. The pedigree testifies to this. It is believed that this is a newly emerged mutation, the ancestor of which was a man (or his mother). The disease has now become widespread in this population. If in the world on average there are from 6.6 to 18 patients per 10,000 men, then among Teleuts the incidence of hemophilia is 3 people per 1,000 men, which is hundreds of times higher than the world level. Thus, we can talk about the high accumulation of the hemophilia gene in the Teleut population. A serious danger arises for this nationality, since its number is only 3.5 thousand people.

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Answer the questions What are the chromosomes that are the same in both sexes called? Which chromosomes are called sex or heterochromosomes? What determines the sex of the future offspring? Which sex is called homogametic and why? Which sex is called heterogametic? What sex is homogametic in humans, most vertebrates, many insects, and dioecious plants? What sex is homogametic in birds, butterflies, reptiles, and tailed amphibians? What traits are called sex-linked? Why do male individuals immediately exhibit recessive traits associated with the X chromosome in their phenotype? What are some examples of sex-linked diseases?

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Tasks on the topic “Sex-linked inheritance” Enamel hypoplasia is inherited as a dominant trait linked to the X chromosome. In a family where both parents suffered from this anomaly, a son was born with normal teeth. What will the second son be like? In humans, pseudohypertrophic muscular dystrophy ends in death at 10–20 years of age. In some families, the disease is influenced by a sex-linked recessive gene. The disease has been reported only in boys. If affected boys die before childbearing, why does this disease not disappear from the population? Hypertrichosis (hair growth on the edge of the ear) is inherited as a trait linked to the Y chromosome. What is the probability of having children and grandchildren with this trait in a family where the father and grandfather had hypertrichosis?