Determination of sex in humans. Levels of sex differentiation in development. Determining sex in people How does sex appear in humans?

Recently, for those Americans who are dissatisfied with their gender, the Internet network Facebook offered a choice of registration.

There was a lot of fun on the internet about this. But he who laughs last laughs best. As if the children of laughing people would not have to forcefully try on these gender roles (it would be more correct to call them genders). Reality overtakes the most avant-garde antics like this.

Few people realize that the UN, the European Union, PACE and a host of other influential international organizations have already adopted resolutions, declarations and other documents that not only give the green light to these 58 genders, but also oblige many countries to introduce such gender designations by law.

Cockerel or chicken?

On the eve of the Facebook action, the European Parliament welcomed the “Lunacek report”, named after the Austrian LGBT activist and deputy from the Green Party, with a bang. In essence, she proposed giving representatives of her native LGBT community special rights that would give them advantages over other homo sapiens. They receive unlimited freedom of speech, but they cannot be contradicted. Even parents do not have the right to protect their children from gender propaganda.

So the modern world revolves not only around the dollar, oil or sex, but also around gender. Strictly speaking, the world itself does not rotate around this axis; it is turned by force, like meat in a meat grinder. Laws requiring such a radical restructuring of society are adopted behind the scenes in the most democratic countries. This is done by the untouchable caste - international bureaucracy, concentrated in supranational structures. And then they are imposed on almost all countries.

What is the essence of gender? In the 1970s, this term began to designate one of the hypostases of gender - social. To determine your biological sex, just take off your pants. But social gender is what is in the head, how a person feels about himself, what gender he chose, regardless of whether he was born a boy or a girl. Initially, this was used only in medicine for the treatment and rehabilitation of people with such disorders.

But when radical philosophers, psychologists and anthropologists took up gender, they developed the so-called gender theory. What is its essence? We warn you that further reading is not for the faint of heart. According to gender theory, a child is born not as a boy or a girl, but as something indeterminate; he has the makings of all genders at once, regardless of whether he actually has a “cockerel” or a “hen.” And we become men and women only because we are raised that way. The main role, of course, is played by the family - from century to century, “gender violence” (this is the official term) is reproduced against the individual, imposing on the boy the role of a man, and on the girl the role of a woman and mother. This dictatorship of the family must be destroyed. Hence, juvenile justice, the fight against so-called domestic violence, radical forms of protecting the rights of the child, and other actively sponsored technologies for family destruction - they all play on the side of gender theory and practice.

In the United States, a book called “It's Totally Normal” is recommended for reading in 4th grade. One of the pages talks about how it's okay to be gay or lesbian. Photo: Collage AiF

Lessons for youngsters

Gender pedagogy recommends that children try themselves in different roles, emphasizing that unconventionality is great. It is better to start doing this in elementary school or even in kindergarten, when the child begins to realize his biological sex - the optimal age to create gender chaos in a child’s head.

This is called "gender equality" education and is practiced in many countries in northern Europe and is being imposed on countries that have recently joined the EU. In a camouflaged form, it leaks out in the form of sex education for young children. After such lessons, girls often begin to play at war, and boys - at gays, transvestites or daughter-mothers.

But after the “Lunacek report”, such education may become practically mandatory, and parents will no longer be able to protect their child from these lessons. By the way, conflicts are already arising in Germany, where parents who protect their children are even subject to criminal penalties. Is this hard for you to believe? All this seems like nonsense that cannot happen because it can never happen? I understand your logic, but I remind you: the relevant agreements are already enshrined in official documents, signed by hundreds of countries, and are being implemented in practice in many regions.

How could this happen? Quiet and unnoticeable. The term “gender” first appeared in documents in 1995 in the so-called UN Beijing Declaration. And then it only meant the need to introduce equality between men and women. At that time, few people argued with this statement, and the document was accepted with enthusiasm. But it turned out that women seemed to be simply used to quietly push all representatives of the LGBT community under the gender umbrella. And as you already know, they needed equality even more than women.

The number of 58 genders identified by experts for the Facebook campaign is arbitrary. According to gender theory, there may be more of them. You can essentially distinguish them endlessly, inventing microscopic differences. For example, the most common ones are those for which the acronym LGBT is used: its letters stand for homosexual genders (lesbians, gays, bisexuals) and transgenders - these are those who are dissatisfied with their biological sex. There are many of them: transsexuals seek to change their sex surgically, transvestites simply dress up in clothes of the opposite sex, androgynes combine male and female traits and behavior, hermaphrodites have male and female genital organs, bigenders change sexual behavior depending on the circumstances, agenders deny any floor. The list goes on, as they did on Facebook. On the sidelines, the introduction of new genders is being discussed, based on incest and pedophilia.

Biological and social factors influencing gender identification are so closely related that it is difficult to understand them. When a child is born to parents, in modern times it is already known in advance what gender it will be, but if the mother did not know this before giving birth. What a thirst she would have then to find out the sex of the baby as quickly as possible. This happens because parents treat their children differently depending on their gender. Thus, the behavior of mom and dad gives the child an incentive to learn more about himself by identifying himself by gender.

After conception, the process of formation of sexual characteristics in the embryo occurs. Having united, the female and male cells combine their chromosomes, 23 each from the sperm and egg into a new organism. This gives a total of 46 chromosomes. A female cell always carries an X chromosome, and a male spermatozoon either Y or X. Thus, the female code is XX, and the male XY is male.

Further in the development of the embryo, the stage of formation of the gonads takes place. This occurs in the sixth week of pregnancy. Before this period, it is impossible to determine the fetus. A male embryo occurs when a male chromosome is present. The H-Y antigen, which is responsible for the male genetic code, must be present here. The absence of this antigen indicates that the sex of the child will be female.

The appearance of the genital organs occurs after the stage of formation of the gonads with the help of hormones. This stage begins at 8-9 weeks of pregnancy. When the amount of testosterone produced is greater, the gender is determined to be male. Both female and male bodies contain hormones of both sexes, however, a greater amount of a particular hormone indicates a specific gender.

The process of intrauterine development of the fetus involves the influence of androgens on it (hormones that play a decisive role in the occurrence of secondary sexual characteristics in both one and the other sex, for example, a rough voice, “vegetation” on the face and the whole body. As in all men, increased secretion sweat, elongation of the penis, formation of the face and body skeleton according to the male type, increase in the size of the prostate and the amount of its secretion). If androgens do not have a sufficient effect on the fetus, then a girl will be born. In the first period, the formation of the genital organ occurs. Then comes the creation of the brain's sexual orientation. The stage of formation of the male or female hypothalamus is underway.

Laying of external organs

In the seventh week, organs specific to a particular sex undergo changes under the influence of sex hormones.
In the female fetus, steroid hormones form the labia, and in the male fetus, the penis. The genital tubercle becomes the penis in men and the clitoris in women.
At the beginning of the 3rd month, the vaginal slit opens in girls and the length of the penis increases in boys. 11-12 weeks is the period when it is possible to accurately distinguish one sex from another based on sexual characteristics; in a fetus with XY chromosomes, the median suture becomes overgrown.

Laying the internal organs:

During the initial 6 weeks of pregnancy, male and female embryos cannot be distinguished;
Only after 8 weeks of pregnancy, the testes of an embryo with the sexual characteristics of a boy release testosterone and an inhibitor of the Müllerian ducts, leading to the disappearance of the ducts themselves. In the absence of male hormones, the Müllerian ducts (a double canal with a connected distal part, which appears after the end of the second month of development of the embryo inside the mother from the grooves that serve as the demarcating role of the epithelium) begin to transform into female organs. The Wolffian ducts (structures in the fetus that subsequently develop into the male genital organs located inside) cease to exist.
After 9 months of pregnancy, in the female fetus, the Müllerian duct turns into the fallopian tubes, and in the male fetus, the glands turn into the scrotum.

Video of how the sex of a child is determined

Our cells. Chromosomes determine everything from hair color and eye color to gender. Whether you are a man or a woman depends on the presence or absence of certain chromosomes. Humans contain 23 pairs or a total of 46 chromosomes.

There are 22 pairs of autosomes (non-sex chromosomes) and one pair of gonosomes (sex chromosomes). The sex chromosomes are the X and Y chromosomes.

Sex cells

During human sexual reproduction, two separate gametes fuse to form a zygote. - these are produced by a type of cell division called. They contain only one set of chromosomes and are called .

The male gamete, called the sperm, is relatively mobile and usually has a . The female gamete, called the egg, is immobile and relatively large compared to the male gamete. When haploid male and female gametes combine in a process called fertilization, they develop into a zygote. It is a zygote, meaning that it contains two sets of chromosomes.

Sex chromosomes XY

Male gametes, or sperm, in humans and other mammals are heterogametic and contain one of two types of sex chromosomes.

Sperm cells carry X or Y chromosomes. However, female gametes or eggs contain only the X chromosome and are homogametic. In this case, the sperm cell determines the sex of the individual. If a sperm cell containing an X chromosome fertilizes an egg, the resulting zygote will be XX - female. If the sperm cell contains a Y chromosome, then the resulting zygote will be XY - male.

Y chromosomes carry those necessary for male or testicular development. Individuals lacking a Y chromosome (XO or XX) develop female gonads or ovaries. Two X chromosomes are required for the development of fully functioning ovaries.

Genes located on the X chromosome are called X-linked genes, and they determine X-linked recessive inheritance. A mutation occurring in one of these genes can result in the development of altered traits. Since males only have one X chromosome, the altered trait will always be expressed in males. In females, the trait will not always be expressed, since they have two X chromosomes. The altered trait may be masked if only one X chromosome has the mutation and the trait is recessive.

Sex chromosomes XX

Grasshoppers, cockroaches and other insects have a sex determination system similar to humans. Adult males lack the Y sex chromosome and only have an X chromosome. They produce sperm cells that contain the X chromosome or a sexless chromosome called O. Females are XX and produce eggs that contain the X chromosome.

If an X sperm cell fertilizes an egg, the resulting zygote will be XX - female. If a sperm cell that does not contain a sex chromosome fertilizes an egg, the resulting zygote will be XO - male.

Sex chromosomes ZW

Birds, insects such as butterflies, frogs, snakes and some fish species have different sex determination systems. In these animals, it is the female gamete that determines sex. Female gametes can contain either a Z chromosome or a W chromosome. Male gametes contain only a Z chromosome. In these species, the chromosome combination ZW means female, and ZZ means male.

Parthenogenesis

What about animals like most species of wasps, bees and ants that do not have sex chromosomes? How is gender determined? In these species, sex is determined. If the egg is fertilized, a female will emerge from it. An unfertilized egg may produce a male. The female is diploid and contains two sets of chromosomes, while the haploid male contains only one set of chromosomes. This development of a male from an unfertilized egg and a female from a fertilized egg is a type of parthenogenesis known as arrhenotocous parthenogenesis.

Ecological sex determination

In turtles and crocodiles, sex is determined by the ambient temperature during a certain period of development of the fertilized egg. Eggs that are incubated above a certain temperature develop into one sex, and eggs that are incubated below a certain temperature develop into the other sex.

Remember!

What is the ratio of men to women in the human population?

Sex ratio is the ratio of the number of males to the number of females in a dioecious population. Sex ratio, along with sexual dimorphism, is an important characteristic of a dioecious population. It is usually expressed as the number of males per 100 females, the proportion of males, or as a percentage. Depending on the stage of ontogenesis, primary, secondary and tertiary sex ratios are distinguished. Primary is the sex ratio in zygotes after fertilization; secondary - the sex ratio at birth and, finally, tertiary - the sex ratio of mature individuals capable of reproducing in the population.

What organisms are called hermaphroditic?

Hermaphroditism is the simultaneous or sequential presence of male and female sexual characteristics and reproductive organs in an organism.

Review questions and assignments

1. Which chromosomes are called sex chromosomes?

Sex chromosomes are chromosomes that can be used to distinguish individuals of different sexes from each other.

2. What are autosomes?

Autosomes are the chromosomes of somatic cells.

3. What is homogametic and heterogametic sex? Is the male sex always heterogametic?

Homogametic sex is a sex in which the sex chromosomes are paired homologous (identical in shape and structure), for example, the female sex of mammals and humans, which is characterized by paired sex chromosomes XX. Heterogametic sex is a sex in which the sex chromosomes are unpaired, non-homologous (different), for example, the male sex of mammals and humans, which is characterized by unpaired XY sex chromosomes. No not always. For example, in birds, females have heterogametic sex, and males have homogametic sex.

4. When does genetic determination of sex occur in humans and what causes this?

During the process of spermatogenesis, a male Drosophila will equally likely produce two types of gametes, containing X- and Y-chromosomes, i.e., the male sex of Drosophila is heterogametic (from the Greek heteros - different, other). During fertilization, if an egg fuses with a sperm containing an X chromosome, a pair of XX sex chromosomes is formed and a female is formed. If the sperm contained a Y chromosome, it would develop into a male. The sex of the future individual is determined at the moment of fertilization and depends on the set of sex chromosomes. The same mechanism is used to determine sex in humans. Women have the same sex chromosomes, they are called X chromosomes; men have one X chromosome and one Y chromosome. The remaining 22 pairs of chromosomes are the same in men and women; these are autosomes. Consequently, the sex of the baby depends on which sperm fertilizes the egg. Initially, the human embryo is bisexual, but the presence of the Y chromosome directs the development of the yet undifferentiated genital organs of the fetus according to the male type, turning them into testes. The Y chromosome contains a special gene that causes this specialization at 4-8 weeks of the embryonic period. In the absence of the Y chromosome, the embryo develops according to the female type.

5. What mechanisms of sex determination do you know? Give examples.

The belonging of individuals to one sex or another can be determined not only at the moment of fertilization, as happens in most organisms. Sometimes sex is determined by environmental influences after fertilization. For example, in the sea worm Bonnelia, the sex of the larva will depend on the place where it ends up after the completion of the free swimming period. If it, settling to the bottom, falls on the body of an adult female, a male will form from it under the influence of chemicals secreted by the female. If the larva settles to the bottom and there is no mature female nearby, it turns into a female. There are other mechanisms for determining sex, for example, in grasshoppers, females have two identical sex chromosomes (XX), and males have only one (X0). In bees, female individuals (queens and worker bees) develop from dipid fertilized eggs (2n), and male individuals (drones) develop from unfertilized ones (1n), the chromosome set of which doubles in the process of individual development.

6. Explain what sex-linked inheritance is.

Mendel's experiments show the peculiarities of inheritance of traits whose genes are located in non-sex chromosomes - autosomes. In this case, inheritance occurs regardless of which parent (mother or father) had one or another genotype. If, as a female individual, we take a pea plant grown from a yellow seed and pollinate it with pollen from a plant grown from a green pea, or we could do the opposite, and the result of the crossing would remain unchanged. However, the situation changes dramatically if traits whose genes are located on the sex chromosomes are inherited. This type of inheritance is called sex-linked inheritance. Genes located on the Y chromosome are passed on only through the male line, from father to son, so the traits for which they are responsible are absent in women. In addition to the aforementioned gene responsible for the differentiation of the gonads, the Y chromosome contains genes that control early baldness, increased ear hairiness, and the development of webbing between the toes. The X chromosome contains a gene that determines blood clotting. Its recessive allele causes a serious disease - hemophilia. In addition, the X chromosome contains genes that affect the size and shape of teeth, the development of color blindness (the inability to distinguish between green and red), optic nerve atrophy and many other signs. The X chromosome and Y chromosome contain different genes, i.e. they are not homologous chromosomes, this determines the inheritance of sex-linked traits.

7. How is color blindness inherited? What color perception will children have whose mother is colorblind and whose father has normal vision?

It was found that color blindness is caused by a recessive allele (Хd), normal color perception is caused by a dominant allele (ХD), therefore women heterozygous for this gene (ХДХd) had normal vision. Let's consider what kind of children can be born to a woman who is a carrier of the color blindness gene (ХДХd), married to a man with normal color perception (ХDY). A woman will give half of her sons and daughters an X chromosome with the gene for color blindness (Xd), and half an X chromosome with the gene for normal color perception (XD). At the same time, all daughters will receive from their father a second X chromosome with the gene for normal color perception (XD), so they will all have normal vision, but half of them will be carriers of the recessive gene for color blindness received from their mother (1XDXD: 1XDXd). All sons will receive a Y chromosome from their father, and half of them will be color blind (1XDY: 1XdY).

Think! Remember!

1. Explain from the perspective of genetics why there are many more colorblind people among men than among women.

The genotype of men with this disease can only be of two types: XDY (healthy) or XdY (sick), since men have only one X chromosome (50% chance). And women have two genotypes: XDXd (healthy carrier), XDXD (healthy), XdXd (sick), the probability of such genotypes is 33.3%. Moreover, the appearance of such a girl ХdХd (sick) is possible only if the father is sick and the mother is a carrier - this probability is extremely low, so the appearance of color-blind boys is much more common.

2. Many young husbands want their first child to be a son, and after the birth of their daughter they blame their wives for not living up to their expectations. Do you think their claims have any basis?

No. During fertilization, if an egg fuses with a sperm containing an X chromosome, a pair of XX sex chromosomes is formed and a girl is formed. If the sperm contained a Y chromosome, it would develop into a boy. The sex of the future individual is determined at the moment of fertilization and depends on the set of sex chromosomes.

Two basic rules for determining sex in mammals.

Classic embryogenetic studies have established two rules for determining sex in mammals. The first of them was formulated in the 60s by Alfred Jost based on experiments on removing the rudiment of future gonads (gonadal ridge) from early rabbit embryos: removal of the ridges before gonad formation resulted in all embryos developing as females. It has been suggested that the male gonads (testis) secrete an effector (Testosterone) responsible for the masculinization of fetuses, and the presence of a second effector anti-Müllerian hormone (MIS) has been predicted to directly control such anatomical transformations. The results of the observations were formulated in the form of a rule: the specialization of the developing gonads into the testis or ovary determines the subsequent sexual differentiation of the embryo. Until about 1959, it was assumed that the number of X chromosomes, known to be two in females and one in males, was the most important factor in the control of sex in mammals. However, the discovery of individuals with a single X chromosome developing as females, and individuals with a single Y chromosome and multiple X chromosomes developing as males, has led to the abandonment of such ideas. The second rule for determining sex in mammals has been formulated: The Y chromosome carries the genetic information required for sex determination in males. The combination of the above two rules is sometimes called the growth principle: Chromosomal sex, associated with the presence or absence of the Y chromosome, determines the differentiation of the embryonic gonad, which in turn controls the phenotypic sex of the organism. This mechanism of sex determination is called genetic (GSD) and is contrasted with that based on the controlling role of environmental factors (ESD) or the ratio of sex chromosomes and autosomes (CSD).

Physiological basis of the gonadal level of sex determination.

The physiological basis of the mechanism of sex determination is the bisexuality of the embryonic gonads of mammals. In such progonadas, the Müllerian duct and Wolffian canal are simultaneously present - the rudiments of the reproductive tract of females and males, respectively. Primary sex determination begins with the appearance of specialized cell lines in the progonads - Sertoli cell. In the latter, the MIS predicted by Jost is synthesized, which is responsible for direct or indirect inhibition of the development of the Müllerian duct - the rudiment of the future fallopian tubes and uterus.

Genetic mechanism of sex determination.

Human Y chromosome indicating the location of the SRY gene

In 1987, David Page and his colleagues, studying male XX, who inherited 280 kb. fragment of Y-chromosome-specific DNA, and an XY woman with a deletion (deficiency) involving this region as a result of the exchange of sections between chromosomes, seemed to have discovered an escaped TDF. It turned out to be present in the Y chromosome of all true Eutheria animals and located in a region measuring 140 kb. at 100 kb from the border of the pseudoautosomal region, the ZFY gene. The homolog ZFY - ZFX is found on the X chromosome, and it avoids the inactivation characteristic of genes localized in it. Both of these factors encode a protein that forms a so-called zinc finger structure, has DNA-binding activity, and can be considered a transcription factor. Further detailed analysis of Y chromosome-specific sequences in sex-reversed individuals limited the search to a region of 35 kb. and led to the discovery of a gene considered to be a true equivalent to classical TDF. This gene is called SRY ( Sex determining Region Y gene). Let us present some of its characteristics that force us to take this assumption into account. SRY is located in the sex-determining region and contains a conserved domain (HMG box) encoding a protein of 80 amino acid residues in size. Its activity was noted on the eve of the period of differentiation of the progonade into the testis - the 10-12th day of embryonic development in the mouse and, at least at this stage, does not depend on the presence of germ cells. Specific point mutations or deletions in the HMG box of this gene in XY women lead to sex inversion. Transfer of 14 kb. a DNA fragment containing this gene with flanking regions into the fertilized egg of a homogametic individual using microinjection (a procedure of transgenesis - gene transfer) led to the appearance of a male with an XX karyotype. True, this animal has defective spermatogenesis.

Functions of the SRY gene.

The domain encoded by the HMG box of the SRY gene specifically binds to DNA, leading to the bending of its molecule. Such deformation of the DNA structure, induced by the SRY protein or related molecules (more than 100 proteins with an HMG domain are known), can be mechanically transmitted over a distance and play an important role in the regulation of transcription, replication and recombination. The region of DNA in which SRY is localized is responsible for encoding two key enzymes involved in the differentiation of the primary gonad into the male type: P450 aromatase, which controls the conversion of testosterone to estradiol and a factor or hormone that inhibits the development of Miller's ducts, which causes their reverse development and promotes differentiation testicle SRY is also involved in the processes of sexual differentiation in close interaction with another gene, named by K. McElreavey et al. (1993) genome Z, whose normal function is to suppress specific male genes. In the case of the normal male genotype 46XY, the SRY gene produces a protein that inhibits the Z gene, and specific male genes are activated. In the case of the normal female genotype 46XX, in which SRY is absent, the Z gene is activated and inhibits a specific male gene, which creates conditions for female-type development.