On whom and on what does the sex of the unborn child at conception depend: on chance, man or woman? Structure, development, and division of male and female germ cells. Formation of germ cells.

These cells differ significantly between men and women. In men, germ cells or sperm have tail-like projections () and are relatively mobile. Female reproductive cells, called eggs, are immobile and much larger than male gametes. When these cells fuse in a process called fertilization, the resulting cell (zygote) contains a mixture of what is inherited from the father and mother. Human sex organs are produced by the organs of the reproductive system - the gonads. produce sex hormones necessary for the growth and development of primary and secondary reproductive organs and structures.

The structure of human germ cells

Male and female reproductive cells differ greatly in size and shape. Male sperm resemble long, mobile projectiles. These are small cells that consist of a head, middle and tail parts. The head contains a cap-like covering called an acrosome. The acrosome contains enzymes that help the sperm cell penetrate the outer membrane of the egg. located in the head of the sperm. The DNA in the nucleus is tightly packed and the cell does not contain much. The middle part contains several mitochondria that provide energy for. The tail consists of a long projection called a flagellum, which aids in cellular locomotion.

A woman's eggs are one of the largest cells in the body and have a round shape. They are produced in the female ovaries and consist of a nucleus, a large cytoplasmic region, a zona pellucida and a corona radiata. The zona pellucida is a membrane covering that surrounds the eggs. It binds sperm cells and helps in fertilization. The corona radiata is the outer protective layer of follicular cells surrounding the zona pellucida.

Formation of germ cells

Human germ cells are produced through a two-step process of cell division called. Through a series of sequential events, the replicated genetic material in the parent cell is distributed among the four daughter cells. Since these cells have half the number of the parent cell, they are . Human germ cells contain one set of 23 chromosomes.

There are two stages of meiosis: meiosis I and meiosis II. Before meiosis, chromosomes are replicated and exist in the form. At the end of meiosis I, two are formed. The sister chromatids of each chromosome in the daughter cells are still linked. At the end of meiosis II, sister chromatids and four daughter cells are formed. Each cell contains half the chromosomes of its parent cell.

Meiosis is similar to the process of division of non-reproductive cells known as mitosis. produces two daughter cells that are genetically identical and contain the same number of chromosomes as the parent cell. These cells are diploid because they contain two sets of chromosomes. Humans include 23 pairs or 46 chromosomes. When germ cells unite during fertilization, the haploid cell becomes a diploid cell.

The production of sperm is known as spermatogenesis. This process occurs continuously inside the male testicles. Hundreds of millions of sperm must be released for this to happen. The vast majority of sperm do not reach the egg. During oogenesis, or egg development, daughter cells divide unevenly in meiosis. This asymmetric cytokinesis results in the formation of one large egg (oocyte) and smaller cells called polar bodies, which degrade and are not fertilized. After meiosis I, the egg is called a secondary oocyte. The secondary oocyte will complete the second stage of meiosis if the fertilization process begins. Once meiosis II is completed, the cell becomes an egg and can fuse with a sperm cell. When fertilization is complete, the combined sperm and egg become a zygote.

Sex chromosomes

Male sperm in humans and other mammals are heterogametic and contain one of two types of sex chromosomes: X or Y. However, female eggs contain only the X chromosome and are therefore homogametic. Sperm of an individual. If a sperm cell containing an X chromosome fertilizes an egg, the resulting zygote will be XX or female. If the sperm cell contains a Y chromosome, then the resulting zygote will be XY or male.

Ecology of life. Science and discoveries: Modern science continues to develop strategies to combat extra chromosomes...

Is 46 normal?

Unlike teeth, a person is supposed to have a strictly defined number of chromosomes - 46 pieces. However, upon closer examination, it turns out that each of us may be a carrier of extra chromosomes.

Where do they come from, where do they hide and what harm do they cause (or maybe benefit?) - let’s figure it out with the participation of modern scientific literature

Subsistence optimum

First, let's agree on terminology. Human chromosomes were finally counted a little more than half a century ago - in 1956. Since then, we know that in somatic, that is, not germ cells, there are usually 46 of them - 23 pairs.

Chromosomes in a pair(one received from the father, the other from the mother) is called homologous. They contain genes that perform the same functions, but often differ in structure. The exception is the sex chromosomes - X And Y , the gene composition of which does not completely coincide. All other chromosomes, except sex chromosomes, are called autosomes.

The number of sets of homologous chromosomes - ploidy - in germ cells is one, and in somatic cells, as a rule, two.

B chromosomes have not yet been discovered in humans. But sometimes an additional set of chromosomes appears in cells - then they talk about polyploidy, and if their number is not a multiple of 23 - about aneuploidy. Polyploidy occurs in certain types of cells and contributes to their increased functioning, while aneuploidy usually indicates disturbances in the functioning of the cell and often leads to its death.

We must share honestly

Most often, an incorrect number of chromosomes is a consequence of unsuccessful cell division. In somatic cells, after DNA duplication, the maternal chromosome and its copy are linked together by cohesin proteins. Then kinetochore protein complexes sit on their central parts, to which microtubules are later attached. When dividing along microtubules, kinetochores move to different poles of the cell and pull chromosomes with them. If the crosslinks between copies of a chromosome are destroyed ahead of time, then microtubules from the same pole can attach to them, and then one of the daughter cells will receive an extra chromosome, and the second will remain deprived.

Meiosis also often goes wrong. The problem is that the structure of linked two pairs of homologous chromosomes can twist in space or separate in the wrong places. The result will again be an uneven distribution of chromosomes. Sometimes the reproductive cell manages to track this so as not to pass the defect on to inheritance.

The extra chromosomes are often misfolded or broken, which triggers the death program. For example, among spermatozoa there is such selection for quality. But the eggs are not so lucky. All of them are formed in humans even before birth, prepare for division, and then freeze. The chromosomes have already been duplicated, tetrads have been formed, and division has been delayed. They live in this form until the reproductive period. Then the eggs mature in turn, divide for the first time and freeze again. The second division occurs immediately after fertilization. And at this stage it is already difficult to control the quality of division. And the risks are greater, because the four chromosomes in the egg remain cross-linked for decades. During this time, damage accumulates in cohesins, and chromosomes can spontaneously separate. Therefore, the older the woman, the greater the likelihood of incorrect chromosome segregation in the egg.

Meiosis diagram

Aneuploidy in germ cells inevitably leads to aneuploidy of the embryo. If a healthy egg with 23 chromosomes is fertilized by a sperm with extra or missing chromosomes (or vice versa), the number of chromosomes in the zygote will obviously be different from 46. But even if the sex cells are healthy, this does not guarantee healthy development.

In the first days after fertilization, embryonic cells actively divide in order to quickly gain cell mass. Apparently, during rapid divisions there is no time to check the correctness of chromosome segregation, so aneuploid cells can arise. And if an error occurs, then the further fate of the embryo depends on the division in which it happened. If the balance is disturbed already in the first division of the zygote, then the entire organism will grow aneuploid. If the problem arose later, then the outcome is determined by the ratio of healthy and abnormal cells.

Some of the latter may continue to die, and we will never know about their existence. Or it can take part in the development of the organism, and then it will turn out to be mosaic - different cells will carry different genetic material. Mosaicism causes a lot of trouble for prenatal diagnosticians.

For example, if there is a risk of having a child with Down syndrome, sometimes one or more cells of the embryo are removed (at a stage when this should not pose a danger) and the chromosomes in them are counted. But if the embryo is mosaic, then this method becomes not particularly effective.

Third wheel

All cases of aneuploidy are logically divided into two groups: deficiency and excess of chromosomes. The problems that arise with a deficiency are quite expected: minus one chromosome means minus hundreds of genes.

The location of chromosomes in the human cell nucleus (chromosomal territories)

If the homologous chromosome works normally, then the cell can get away with only an insufficient amount of the proteins encoded there. But if some of the genes remaining on the homologous chromosome do not work, then the corresponding proteins will not appear in the cell at all.

In the case of an excess of chromosomes, everything is not so obvious. There are more genes, but here - alas - more does not mean better.

Firstly, excess genetic material increases the load on the nucleus: an additional strand of DNA must be placed in the nucleus and served by information reading systems.

Scientists have found that in people with Down syndrome, whose cells carry an extra 21st chromosome, the functioning of genes located on other chromosomes is mainly disrupted. Apparently, an excess of DNA in the nucleus leads to the fact that there are not enough proteins to support the functioning of chromosomes for everyone.

Secondly, the balance in the amount of cellular proteins is disrupted. For example, if activator proteins and inhibitor proteins are responsible for some process in a cell, and their ratio usually depends on external signals, then an additional dose of one or the other will cause the cell to stop responding adequately to the external signal.

Finally, an aneuploid cell has an increased chance of dying. When DNA is duplicated before division, errors inevitably occur, and the cellular repair system proteins recognize them, repair them, and start doubling again. If there are too many chromosomes, then there are not enough proteins, errors accumulate and apoptosis is triggered - programmed cell death. But even if the cell does not die and divides, then the result of such division will also most likely be aneuploids.

You will live

If even within one cell aneuploidy is fraught with malfunctions and death, then it is not surprising that it is not easy for an entire aneuploid organism to survive. At the moment, only three autosomes are known - 13, 18 and 21, trisomy for which (that is, an extra third chromosome in cells) is somehow compatible with life. This is likely due to the fact that they are the smallest and carry the fewest genes. At the same time, children with trisomy on the 13th (Patau syndrome) and 18th (Edwards syndrome) chromosomes live at best up to 10 years, and more often live less than a year. And only trisomy on the smallest chromosome in the genome, the 21st chromosome, known as Down syndrome, allows you to live up to 60 years.

People with general polyploidy are very rare. Normally, polyploid cells (carrying not two, but from four to 128 sets of chromosomes) can be found in the human body, for example, in the liver or red bone marrow. These are usually large cells with enhanced protein synthesis that do not require active division.

An additional set of chromosomes complicates the task of their distribution among daughter cells, so polyploid embryos, as a rule, do not survive. Nevertheless, about 10 cases have been described in which children with 92 chromosomes (tetraploids) were born and lived from several hours to several years. However, as in the case of other chromosomal abnormalities, they lagged behind in development, including mental development.

However, mosaicism comes to the aid of many people with genetic abnormalities. If the anomaly has already developed during the fragmentation of the embryo, then a certain number of cells may remain healthy. In such cases, the severity of symptoms decreases and life expectancy increases.

Gender injustices

However, there are also chromosomes, the increase in the number of which is compatible with human life or even goes unnoticed. And these, surprisingly, are sex chromosomes. The reason for this is gender injustice: approximately half of the people in our population (girls) have twice as many X chromosomes as others (boys). At the same time, the X chromosomes not only serve to determine sex, but also carry more than 800 genes (that is, twice as many as the extra 21st chromosome, which causes a lot of trouble for the body). But girls come to the aid of a natural mechanism for eliminating inequality: one of the X chromosomes is inactivated, twists and turns into a Barr body. In most cases, the choice occurs randomly, and in some cells the result is that the maternal X chromosome is active, while in others the paternal one is active.

Thus, all girls turn out to be mosaic, because different copies of genes work in different cells.

A classic example of such mosaicism is tortoiseshell cats: on their X chromosome there is a gene responsible for melanin (the pigment that determines, among other things, coat color). Different copies work in different cells, so the coloring is spotty and is not inherited, since inactivation occurs randomly.

Tortoiseshell cat

As a result of inactivation, only one X chromosome always works in human cells. This mechanism allows you to avoid serious troubles with X-trisomy (XXX girls) and Shereshevsky-Turner syndrome (XO girls) or Klinefelter (XXY boys). About one in 400 children is born this way, but vital functions in these cases are usually not significantly impaired, and even infertility does not always occur.

It is more difficult for those who have more than three chromosomes. This usually means that the chromosomes did not separate twice during the formation of sex cells. Cases of tetrasomy (ХХХХ, ХХYY, ХХХY, XYYY) and pentasomy (XXXXX, XXXXY, XXXYY, XXYYY, XYYYY) are rare, some of them have been described only a few times in the history of medicine. All of these options are compatible with life, and people often live to an advanced age, with abnormalities manifested in abnormal skeletal development, genital defects, and decreased mental abilities.

Typically, the additional Y chromosome itself does not significantly affect the functioning of the body. Many men with the XYY genotype do not even know about their peculiarity. This is due to the fact that the Y chromosome is much smaller than the X and carries almost no genes that affect viability.

Sex chromosomes have another interesting feature. Many mutations of genes located on autosomes lead to abnormalities in the functioning of many tissues and organs. At the same time, most gene mutations on sex chromosomes manifest themselves only in impaired mental activity. It turns out that sex chromosomes largely control brain development. Based on this, some scientists hypothesize that they are responsible for the differences (however, not fully confirmed) between the mental abilities of men and women.

Who benefits from being wrong?

Despite the fact that medicine has been familiar with chromosomal abnormalities for a long time, recently aneuploidy continues to attract the attention of scientists. It turned out that more than 80% of tumor cells contain an unusual number of chromosomes. On the one hand, the reason for this may be the fact that proteins that control the quality of division are able to slow it down. In tumor cells, these same control proteins often mutate, so restrictions on division are lifted and chromosome checking does not work.

On the other hand, scientists believe that this may serve as a factor in the selection of tumors for survival. According to this model, tumor cells first become polyploid, and then, as a result of division errors, they lose different chromosomes or parts thereof. This results in a whole population of cells with a wide variety of chromosomal abnormalities. Most are not viable, but some may succeed by chance, for example if they accidentally gain extra copies of genes that trigger division or lose genes that suppress it. However, if the accumulation of errors during division is further stimulated, the cells will not survive.

Action is based on this principle taxol - a common cancer drug: it causes systemic chromosome nondisjunction in tumor cells, which should trigger their programmed death.

It turns out that each of us may be a carrier of extra chromosomes, at least in individual cells. However, modern science continues to develop strategies to deal with these unwanted passengers. One of them suggests using proteins responsible for the X chromosome and targeting, for example, the extra 21st chromosome of people with Down syndrome. It is reported that this mechanism was activated in cell cultures.

So, perhaps, in the foreseeable future, dangerous extra chromosomes will be tamed and rendered harmless.

Morris syndrome (testicular feminization syndrome). Examples of sexual reproduction. Gonadal sex. In reptiles, sex depends on temperature. Gonad. Examples of true hermaphroditism. In humans and other mammals, the homogametic sex is female. Uterus. Sexual dimorphism is better expressed in “harem” species. Hormonal and gametic sex. Testis. Phenotype. An example of hormone disruption. Examples of false hermaphroditism (pseudohermaphroditism).

“Genetics of sex” - A larva without sexual characteristics. Let's try to solve the inheritance problem ourselves. Genes whose expression is limited by gender. The genotype is a single integral system. Sex is a set of characteristics and properties of an organism. X and Y chromosomes. Somatic cells of the body. Why are girls born in some cases and boys in others? What causes independent inheritance of traits? Sex can be determined before fertilization through gametogenesis.

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

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

“Methods of genetic analysis” - Life. Basics of genetic analysis. Literature. Color. Rule of purity of gametes. Karyotype. Mendel's laws. Phenotype. Serebrovsky Alexander Sergeevich. The trait is determined by at least 5 genes. Sign. Second generation analysis. The number of types and combinations of gametes formed. Kirpichnikov Valentin Sergeevich. First generation analysis. Karyotypes of humans and guppies. Genetic analysis algorithm. Number of types formed.

“Laws of Genetics” - Law of Homologous Series. Methods for studying human heredity. Modification variability of dandelion. Basic laws of genetics. Variability. The mechanism of sex determination in Drosophila. Mutational variability. Gregor Johann Mendel. Laws of heredity and variability. Human genetics. An example of solving a problem. Heredity, variability. Monohybrid crossing. Morgan's Law. Modern science.

Sex cells - gametes(from the Greek gametes - “spouse”) can be detected already in a two-week human embryo. They are called primordial germ cells. At this time, they are not at all similar to sperm or eggs and look exactly the same. It is not possible to detect any differences inherent in mature gametes at this stage of embryo development in primary germ cells. This is not their only feature. Firstly, primary germ cells appear in the embryo much earlier than the sex gland itself (gonad), and secondly, they arise at a considerable distance from the place where these glands will form later. At a certain moment, an absolutely amazing process occurs - the primary germ cells rush together to the gonad and populate, “colonize” it.

After the future gametes enter the gonads, they begin to divide intensively, and their number increases. At this stage, germ cells still contain the same number of chromosomes as “bodily” cells ( somatic) cells - 46. However, to successfully carry out their mission, germ cells must have 2 times fewer chromosomes. Otherwise, after fertilization, that is, the fusion of gametes, the cells of the embryo will contain not 46, as established by nature, but 92 chromosomes. It is not difficult to guess that in subsequent generations their number would progressively increase. To avoid this situation, the developing germ cells undergo a special division, which in embryology is called meiosis(Greek meiosis - “decrease”). As a result of this amazing process diploid(from the Greek diploos - “double”), the set of chromosomes is, as it were, “pulled apart” into its constituent single ones, haploid sets (from the Greek haploos - single). As a result, from a diploid cell with 46 chromosomes, 2 haploid cells with 23 chromosomes are obtained. Following this, the final stage of the formation of mature germ cells begins. Now, in a haploid cell, the existing 23 chromosomes are copied and these copies are used to form a new cell. Thus, as a result of the two divisions described, 4 new ones are formed from one primary germ cell.

Moreover, in spermatogenesis(Greek genesis - origin, development) as a result of meiosis, 4 mature sperm with a haploid set of chromosomes appear, and in the process of formation of the egg - in oogenesis (from the Greek oon - “egg”) only one. This happens because the egg cell does not use the second haploid set of chromosomes formed as a result of meiosis to form a new mature germ cell - an oocyte, but “throws” them out as “extra” in a kind of “garbage container”, which is called a polar body. The first division of the chromosome set is completed in oogenesis with the release of the first polar body just before ovulation. The second replication division occurs only after the sperm penetrates the egg and is accompanied by the release of the second polar body. For embryologists, polar bodies are very important diagnostic indicators. There is a first polar body, which means the egg is mature, the second polar body has appeared - fertilization has occurred.

Primary germ cells found in the male gonad do not divide for the time being. Their division begins only during puberty and leads to the formation of a cohort of so-called diploid stem cells, from which sperm are formed. The supply of stem cells in the testicles is constantly replenished. Here it is appropriate to recall the feature of spermatogenesis described above - 4 mature sperm are formed from one cell. Thus, after puberty, a man produces hundreds of billions of new sperm throughout his life.

The formation of eggs proceeds differently. Having barely populated the gonad, the primary germ cells begin to divide intensively. By the 5th month of intrauterine development, their number reaches 6-7 million, but then mass death of these cells occurs. In the ovaries of a newborn girl there are no more than 1-2 million of them, by the age of 7 - only about 300 thousand, and during puberty 30-50 thousand. The total number of eggs that will reach a mature state during puberty will be even less. It is well known that during one menstrual cycle, only one follicle usually matures in the ovary. It is easy to calculate that during the reproductive period, which lasts for women 30 - 35 years old, about 400 mature eggs are formed.

If meiosis in spermatogenesis begins during puberty and is repeated billions of times during a man’s life, in oogenesis the developing female gametes enter meiosis during the period of intrauterine development. Moreover, this process begins almost simultaneously in all future eggs. It begins, but does not end! Future eggs only reach the middle of the first phase of meiosis, and then the division process is blocked for 12 to 50 years! Only with the advent of puberty will meiosis continue in oogenesis, and not for all cells at once, but only for 1-2 eggs monthly. The process of meiotic division of the egg will be completed, as mentioned above, only after its fertilization! Thus, the sperm penetrates into an egg that has not yet completed division and has a diploid set of chromosomes!

Spermatogenesis And oogenesis- very complex and largely mysterious processes. At the same time, their subordination to the laws of interrelation and conditionality of natural phenomena is obvious. To fertilize one egg in vivo(lat. in a living organism) tens of millions of sperm are needed. The male body produces them in gigantic quantities almost throughout his life.

Carrying and giving birth to a child is an extremely difficult burden on the body. Doctors say that pregnancy is a health test. How a child will be born directly depends on the health of the mother. Health, as you know, does not last forever. Old age and illness, unfortunately, are inevitable. Nature gives a woman a strictly limited, irreplaceable number of germ cells. A decrease in fertility develops slowly, but gradually along an incline. We receive clear evidence that this is indeed the case by daily assessing the results of ovarian stimulation in ART programs. Most of the eggs are usually used up by the age of 40, and by the age of 50 their entire supply is completely exhausted. Often the so-called ovarian depletion comes much earlier. It should also be said that the egg is subject to “aging”; over the years, its ability to fertilize decreases, and the process of chromosome division is increasingly disrupted. Having children at a late reproductive age is risky due to the increasing risk of having a child with a chromosomal abnormality. A typical example is Down syndrome, which occurs due to the 21st chromosome remaining during division. Thus, by limiting the reproductive period, nature protects the woman and takes care of healthy offspring.

According to what laws does chromosome division occur? How is hereditary information transmitted? In order to understand this issue, we can give a simple analogy with cards. Let's imagine a young married couple. Let's call them conventionally - He and She. Each of its somatic cells contains chromosomes of the black suit - clubs and spades. He received a set of clubs from six to ace from his mother. A set of spades - from my dad. In each of its somatic cells, red chromosomes are diamonds and hearts. She received a set of diamonds from six to ace from her mother. A set of worms - from my dad.

In order to obtain a sex cell from a diploid somatic cell, the number of chromosomes must be halved. In this case, the sex cell must contain a complete single (haploid) set of chromosomes. Not a single one should get lost! In the case of cards, such a set can be obtained as follows. Take one at random from each pair of black cards and thus form two single sets. Each set will include all cards of the black suit from six to ace, however, what kind of cards these will be (clubs or spades) is determined by chance. For example, in one such set the six may be a spades, and in another it may be a club. It’s not hard to imagine that in the example with cards, with such a choice of a single set from a double set, we can get 2 combinations to the ninth power - more than 500 options!

In the same way, we will make a single set of her red cards. We will get more than 500 different options. From his single and her single set of cards we will make a double set. It will turn out to be, to put it mildly, “variegated”: in each pair of cards, one will be red and the other will be black. The total number of such possible sets is 500×500, that is, 250 thousand options.

Nature does approximately the same thing, according to the law of random sampling, with chromosomes during the process of meiosis. As a result, from cells with a double, diploid set of chromosomes, cells are obtained, each of which contains a single, haploid complete set of chromosomes. Let's say that as a result of meiosis, a sex cell is formed in your body. Sperm or egg - in this case it does not matter. It will definitely contain a haploid set of chromosomes - exactly 23 pieces. What exactly are these chromosomes? Let's take chromosome 7 as an example. This could be the chromosome you received from your father. It could just as likely be a chromosome you got from your mother. The same is true for chromosome No. 8, and for any other.

Since in humans the number of haploid chromosomes is 23, then the number of possible variants of sexual haploid cells formed from diploid somatic cells is equal to 2 to the power of 23. This results in more than 8 million variants! During the process of fertilization, two germ cells unite with each other. Therefore, the total number of such combinations will be 8 million x 8 million = 64,000 billion options! At the level of a pair of homologous chromosomes, the basis of this diversity looks like this. Let's take any pair of homologous chromosomes of your diploid set. You received one of these chromosomes from your mother, but it could be from either your grandmother or your maternal grandfather. You received the second homologous chromosome from your father. However, it can again be, regardless of the first, either the chromosome of your grandmother or your paternal grandfather. And you have 23 pairs of such homologous chromosomes! This results in an incredible number of possible combinations. It is not surprising that one pair of parents gives birth to children who differ from each other in both appearance and character.

By the way, a simple but important conclusion follows from the above calculations. Every person currently living, or who has ever lived in the past on Earth, is absolutely unique. The chances of a second one appearing are almost zero. Therefore, there is no need to compare yourself with anyone. Each of you is unique, and that makes you interesting!

However, let's return to our reproductive cells. Each diploid human cell contains 23 pairs of chromosomes. Chromosomes from 1 to 22 pairs are called somatic and they are the same in shape. The chromosomes of the 23rd pair (sex chromosomes) are the same only in women. They are designated by the Latin letters XX. In men, the chromosomes of this pair are different and are designated XY. In the haploid set of an egg, the sex chromosome is always only X, while the sperm can carry either an X or a Y chromosome. If the egg is fertilized by X sperm, a girl will be born, if Y sperm, a boy will be born. It's simple!

Why does meiosis in an egg take so long? How is a monthly selection of a cohort of follicles that begin their development and how is the leading, dominant, ovulatory follicle selected from them, in which the egg will mature? Biologists do not yet have clear answers to all these difficult questions. The process of formation of mature eggs in humans awaits new researchers!

The formation and maturation of sperm, as already mentioned, occurs in the seminiferous tubules of the male reproductive gland - testicles. The formed sperm has a length of about 50-60 microns. The sperm nucleus is located in its head. It contains the paternal hereditary material. Behind the head is a neck, in which there is a large convoluted mitochondria- an organelle that provides tail movement. In other words, this is a kind of “energy station”. There is a “cap” on the head of the sperm. Thanks to it, the shape of the head is oval. But, it’s not about the form, but about what is contained under the “cap”. This “cap” is actually a container and is called acrosome, and it contains enzymes that are capable of dissolving the shell of the egg, which is necessary for the sperm to penetrate inside - into the cytoplasm of the egg. If the sperm does not have an acrosome, its head is not oval, but round. This sperm pathology is called globulospermia(round-headed sperm). But, again, the trouble is not in shape, but in the fact that such a sperm cannot fertilize an egg, and a man with such a disorder of spermatogenesis was doomed to childlessness until the last decade. Today, thanks to ART, infertility in these men can be overcome, but we will talk about this later in the chapter devoted to micromanipulation, in particular, ICSI.

The movement of the sperm is carried out due to the movement of its tail. The speed of sperm movement does not exceed 2-3 mm per minute. It would seem not much, however, in 2-3 hours in the female reproductive tract, sperm travel a distance 80,000 times greater than their own size! If a person were in the place of the sperm in this situation, he would have to move forward at a speed of 60-70 km/h - that is, at the speed of a car!

The sperm in the testicle are immobile. They acquire the ability to move only by passing through the vas deferens under the influence of the fluids of the vas deferens and seminal vesicles, and the secretion of the prostate gland. In the female genital tract, sperm remain motile for 3-4 days, but they must fertilize the egg within 24 hours. The entire development process from a stem cell to a mature sperm lasts approximately 72 days. However, since spermatogenesis occurs continuously and a huge number of cells enter it at once, the testicles always contain a large number of sperm at different stages of spermatogenesis, and the supply of mature sperm is constantly replenished. The activity of spermatogenesis varies from person to person, but decreases with age.

As we have already said, eggs are in follicles ovary. As a result of ovulation, the egg enters the abdominal cavity, from where it is “caught” by the fimbriae of the fallopian tube and transferred to the lumen of its ampullary section. This is where the egg meets the sperm.

What structure does a mature egg have? It is quite large and reaches 0.11-0.14 mm in diameter. Immediately after ovulation, the egg is surrounded by a cluster of small cells and a gelatinous mass (called radiant crown). Apparently, in this form it is more convenient for the fimbriae of the fallopian tube to capture the egg. In the lumen of the fallopian tube, with the help of enzymes and mechanical action (beating of the cilia of the epithelium), the egg is “cleaned” from the corona radiata. The final release of the egg from the corona radiata occurs after it meets the sperm, which literally stick around the egg. Each sperm secretes an enzyme from the acrosome that dissolves not only the corona radiata, but also acts on the membrane of the egg itself. This shell is called the pellucida, which is what it looks like under a microscope. By secreting the enzyme, all sperm strive to fertilize the egg, but the zona pellucida will allow only one of them to pass through. It turns out that by rushing towards the egg and acting on it collectively, the sperm “clear the way” for only one lucky person. The role of the zona pellucida is not limited to the selection of sperm; in the early stages of embryo development, it maintains the ordered arrangement of its cells (blastomeres). At some point, the zona pellucida becomes tight, it ruptures and hatching(from English hatching - “hatching”) - hatching of an embryo.

It is quite logical that any couple expecting or planning procreation is interested in what determines the sex of the child. Unfortunately, the issue of a baby’s gender is surrounded by illogical myths that contradict common sense and the laws of biology and physiology.

In our article, we will dispel these myths and figure out what determines the gender of a person’s child, and also consider who exactly it depends on – a man or a woman. We will separately touch upon the question of what determines the sex of a child when conceiving a child, and how this process can be influenced.

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Each human somatic cell contains 23 pairs of chromosomes, which carry genetic information - such a set of chromosomes is called diploid (46 chromosomes). 22 pairs are called autosomes and do not depend on the sex of the person; therefore, they are the same in men and women.

The chromosomes of the 23rd pair are called sex chromosomes, since they determine gender. These chromosomes can differ in shape, and they are usually designated by the letters X or Y. If a person has a combination of X and Y chromosomes in the 23rd pair, this is a male individual; if these are two identical X chromosomes, it is female.

Consequently, the cells of the female body have a set of 46XX (46 chromosomes; identical sex X chromosomes), and the male body has a set of 46XY (46 chromosomes; different sex X and Y chromosomes).

Human sex cells, sperm and eggs, contain 23 chromosomes instead of 46 - this set is called haploid. This set of chromosomes is necessary for the formation of a diploid zygote - a cell formed by the fusion of a sperm and an egg, which is the first stage of embryo development. But still, the gender of the child depends on the man. Why? Let's figure it out now.

Chromosome set of man and woman

On whom does it depend more - on a woman or a man?

Many people still ask the question: “Who determines the gender of a child: a woman or a man?” The answer is obvious if you understand which sex chromosomes the sex cells carry.

An egg always has a sex X chromosome, but a sperm can contain both an X and a Y chromosome. If the egg is fertilized by a sperm with an X chromosome, the sex of the baby will be female (23X+23X=46XX). In the case when a sperm with a Y chromosome fuses with an egg, the sex of the child will be male (23X+23Y=46XY). So who determines the gender of the child?

What gender the child will be depends purely on the sperm that fertilizes the egg. It turns out that the gender of the child depends on the man.

What determines the sex of a child at conception? This is a random process when the probability of fertilizing an egg with one or another sperm is approximately the same. The fact that the baby will be a boy or a girl is a coincidence.

Women with feminist inclinations will either have to accept the fact that the gender of the child depends on the man, or women will try long and tediously to influence themselves by modifying their diet, frequency of sexual intercourse and sleep time, without in any way increasing the likelihood of having a boy or a girl. .

Why exactly does a sperm with a Y chromosome fertilize an egg?

On the way to the egg, sperm have many obstacles:

• acidic vaginal environment;
• thick mucus in the cervical canal;
• reverse flow of fluid in the fallopian tubes;
• woman's immune system;
• corona radiata and zona pellucida.

Only one sperm can fertilize an egg, and this sperm can be either a carrier of the X chromosome or the Y chromosome. The position in which sexual intercourse occurs, what diet the man followed, etc. does not affect which sperm will be the “winner”.

There is an opinion that X-sperm are more resistant to the “aggressive” environment in the female genital organs, but at the same time they are slower than Y-sperm, but there is no reliable evidence for this.

Why shouldn’t folk methods and signs be taken seriously?

But because if you include logic and common sense, they have no justification. What are these methods?

1. Ancient calendar methods, for example:
   • Chinese method of sex planning depending on the woman’s age and month of conception;
   • the Japanese method, where the sex of the baby depends on the month of birth of the mother and father;
2. Methods associated with sexual intercourse: abstinence (for the appearance of a girl) and unrestraint (for the appearance of a boy), various positions as a predictor of the male or female gender of the baby;
3. Dietary methods:
   • to get a girl child - foods with calcium (eggs, milk, nuts, beets, honey, apples...);
   • to get a boy child - foods with potassium (mushrooms, potatoes, oranges, bananas, peas...).

Now let’s put everything into pieces.

Chinese and Japanese methods involve the use of special tables to predict the sex of the baby. Who determines the sex of a child at conception? From the sperm that will fertilize the egg. The Chinese stubbornly believed that the sex of the baby depends on the mother, therefore, this method is already devoid of any logical rationale.

Does the sex of the fetus depend on the woman? In any case, the egg contains only the X chromosome, therefore, it is not responsible for whether a girl or a boy is born.

You can rely on the Japanese method if you firmly believe that the compatibility of couples is determined solely by the horoscope, because the essence of this option for determining gender is the same. Let’s remember what determines the sex of the unborn child at conception by studying this method!

Can the dates of birth of two partners influence the fact that after many years the X- or Y-sperm will be the most agile and powerful from a man’s sperm? Especially considering the randomness of the latter. This also includes all kinds of methods that promise the birth of a child of one gender or another depending on the day of the menstrual cycle.

Another way to determine the sex of the unborn child

The pace of sexual activity, as well as diet, can affect the quality of sperm and the likelihood of fertilization, but not the gender of the potential baby.

Modifications of sexual life are not among those factors on which the sex of the unborn child depends, since they cannot speed up movement or increase the endurance of the “same” sperm.

Yes, both X- and Y-spermatozoa differ not in the amount of calcium and potassium, but only in a fragment of a chromosome containing DNA. And there’s no need to talk about a woman’s influence at all - we all remember which parent determines the gender of the child.

Consequently, folk methods of planning the sex of a baby are based on myths and ignorance of the peculiarities of the fertilization process, therefore they cannot be taken seriously. But you will find out what methods you can use to determine pregnancy at home.

Does the sex of the fetus affect the occurrence of toxicosis?

What was previously called toxicosis is now called gestosis. Preeclampsia is the result of pathological adaptation of the female body to pregnancy. The causes of gestosis include disruption of hormonal regulation of pregnancy, immunological changes, hereditary predisposition, peculiarities of placenta attachment and many other factors.

Preeclampsia manifests itself in the form of hemodynamic disorders (for example, increased blood pressure), deterioration of the function of the urinary system (nephropathy of pregnancy, manifested in the form of edema, the appearance of protein in the urine, etc.), in severe cases, a pathology of blood clotting is observed.

To the popular question “Does toxicosis depend on the gender of the unborn child?” There is only one answer: definitely not. None of the factors that cause gestosis can be influenced by the gender of the fetus.

All the first signs of pregnancy are described in detail in. A – it is described at what time and with the help of ultrasound you can reliably find out the sex of the unborn child.

Useful video

It is known that the sex of the unborn child is determined at the moment of conception and depends on which sperm fertilizes the egg. Is this connection random, or can it be influenced in some way:

1. Sperm are produced by the male gonads, which suggests who determines the sex of the unborn child.
2. The fact that an egg can be fertilized by a sperm with both an X and a Y chromosome answers the question why the sex of a child depends on the father and not on the mother.

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