What are the advantages and disadvantages of the phenomenon of hermaphroditism. Hermaphroditism: symptoms, types, causes, diagnostic methods

Hermaphroditismor a violation of sexual differentiation is a whole group of malformations with various clinical manifestations and genetic diversity, characterized by the presence of signs of both sexes in one individual. The term "hermaphroditism" is associated with the ancient Greek myth, according to which the son of two Greek gods - Hermes and Aphrodite - Hermaphrodite was turned into a bisexual creature. Hermaphroditism is otherwise called bisexual, bisexual, androgenic. Natural hermaphroditism occurs naturally in some plant species, in representatives of the coelenterates family, in flatworms, in a number of mollusks and fish.

Distinguish false hermaphroditism, or pseudohermaphroditism, which implies the presence of the external genital organs of both sexes in one organism, and true, or gonadal, hermaphroditism, in which the sex glands of the individual are represented by both the ovaries and the testes. Revealing the form of violation of sexual differentiation allows you to choose the appropriate method for correcting pathology. At the birth of an infant with bisexual external genitalia, karyotyping and ultrasound examination of the pelvic organs are performed to determine the sex of the genital glands, which will make it possible to establish and document the civil sex of the child.

True hermaphroditism is extremely rare. The prevalence of pseudohermaphroditism is approximately 1 in two thousand newborns.

Classification of hermaphroditism

All manifestations of hermaphroditism can be divided into 2 groups - impaired differentiation of the external genital organs and impaired differentiation of the gonads.

Defects in genital differentiation include:

1. Female hermaphroditism characterized by a 46XX karyotype with partial virilization. It occurs with congenital dysfunction of the adrenal cortex or intrauterine virilization of the fetus, associated with the presence of androgen-secreting tumors in a woman, or with the intake of androgenactive drugs.

2. Male hermaphroditism, which is characterized by a 46XY karyotype and inadequate virilization. The emergence of this form of hermaphroditism is facilitated by testicular feminization syndrome, a lack of 5a-reductase and defects in testosterone synthesis.

Gonadal differentiation disorders can manifest themselves in the form of:
- true hermaphroditism;
- Turner syndrome;
- testicular dysgenesis;
- pure agenesis of the gonads.

Causes and mechanism of development of hermaphroditism

The development of hermaphroditism is based on a violation of the normal embryonic development of the fetus due to hereditary or external causes. Hereditary causes can be associated with quantitative and qualitative chromosomal defects in sex chromosomes and autosomes - gene mutations, translocations, deletions. External causes that contribute to the development of hermaphroditism include intoxication, radiation, androgen-producing tumors in the body of a pregnant woman, and the intake of drugs with androgenic activity. The impact of these factors is especially dangerous during critical periods of embryonic development of the fetus (in the seventh to eighth week of pregnancy).

The formation of an individual's sex occurs in several stages. It all begins with the determination of the genetic sex and differentiation of the gonads during intrauterine development, on the basis of which the potential direction of the reproductive function is outlined. After this, a hormonal background is formed with a predominance of male or female sex hormones. The process of the child's sexual identity ends with the formation of the somatic and civil sex, which determines the direction of sex education. Genetic sex determination and the proposed path of gonadal development depend on genes, and the development of the gonads and genitals in the male pattern is determined by factors that are produced by the fetal gonads. Based on this, hermaphroditism can occur as a result of a defect in one of the intrauterine stages of sex formation.

Signs of hermaphroditism

False female hermaphroditism is characterized by a female karyotype 46XX and gonads inherent in the female sex - ovaries. But the external genitals have a bisexual structure. Patients have varying degrees of virilization from a slight increase in the clitoris to the formation of genital organs similar in structure to those of men. The opening to the vagina narrows. Since the disease is most often associated with enzymatic deficiency of 21-hydroxylase and 11-hydroxylase, which is accompanied by impaired potassium-sodium metabolism, patients complain of edema and increased blood pressure.

False male hermaphroditism, otherwise referred to as androgen insensitivity syndrome or testicular feminization syndrome, which is characterized by a 46XY male karyotype against the background of a female phenotype, characterized by spontaneous growth of mammary glands, poor male-type hair growth, absence of the uterus and vaginal aplasia. In this case, the testicles are located in the inguinal canals, labia majora or in the abdominal cavity. If the phenotype has external genital organs similar to normal male ones, then they speak of Reifenstein syndrome.

Occasionally, the cause of male hermaphroditism can be a congenital pathology of testosterone production in the adrenal glands and testicles, which is manifested either by its insufficient secretion or by a disturbed mechanism of action.

Turner syndromeis one of the variants of impaired differentiation of the gonads and is caused by the complete absence of the X chromosome or its structural anomaly. A defect in the X chromosome leads to deformations in the process of expression of genes that control ovarian differentiation and function, which ultimately leads to a disruption in the formation of gonads and the formation of streaks instead. The genes of autosomal chromosomes that control the growth and differentiation of cells of internal organs also undergo transformations, which leads to short stature, the development of a high palate. In addition, the examination of patients reveals ear deformities, a short neck with skin folds on the back in the form of "wings". An instrumental examination of patients reveals heart and kidney defects.

In patients with syndrome of pure gonadal dysgenesis the genitals are usually formed according to the female type, only with the 46XU karyotype is the virilization of the genitals sometimes noted. Growth in patients is normal, external sexual characteristics are not expressed, sexual infantilism is characteristic. In patients with mixed gonadal dysgenesis there is an asymmetric formation of the internal genital organs. Thus, on the one hand, they have a streak, and on the other, a testicle, the functionality of which is preserved.

With true hermaphroditism, which is extremely rare, elements of ovarian and testicular tissue are found in the patient. Signs of this form of hermaphroditism are variable and depend on the activity of the ovarian and testicular tissues. The genitals are bisexual.

Methods for diagnosing hermaphroditism

Diagnosis of the disease consists of the collection and analysis of anamnestic data, examination, instrumental and laboratory research methods.

When collecting an anamnesis, it is important to find out whether the closest maternal relatives had similar disorders. It is necessary to focus on the nature and rate of growth during childhood and puberty, since active growth up to 10 years with its subsequent cessation may indicate adrenal dysfunction as a result of hyperandrogenism. This process can be suspected by the fact of the early appearance of sexual hair growth.

When examining the patient, the physique is assessed, which can inform about the deviations that occur during puberty. For example, the physique of a "eunuch" is formed due to hypogonadism, the basis of which may be hermaphroditism. Short stature, combined with sexual infantilism, allows you to think about Turner syndrome. False male hermaphroditism may be suspected by palpation of the testicles in the labia majora or in the inguinal canals.

Laboratory studies for the diagnosis of hermaphroditism are reduced to the determination of chromosomal and gene mutations using karyotyping and gene studies. Determination of the level of gonadotropins and sex hormones in the blood makes it possible to differentiate hermaphroditism from other diseases. To identify the potential direction of sexual adaptation in patients with a mixed form of gonadal dysgenesis, a test with chorionic gonadotropin is performed. And for the diagnosis of patients with impaired synthesis of testosterone and androgens, the level of testosterone, glucocorticoid and mineralocorticoid hormones, as well as their precursors, is examined, using a stimulation test with analogs of adrenocorticotropic hormone.

With the help of ultrasound and computed tomography, information is obtained about the state of the internal genital organs.

Treatment of hermaphroditism

The main tasks of therapeutic measures for the correction of hermaphroditism are to determine the civil sex and the formation of all the necessary signs for the patient, and to ensure a normal hormonal background. Treatment of patients with hermaphroditism is being developed from surgical sex reassignment and hormone replacement therapy.

Sex reassignment surgery is aimed at the formation of the external genital organs with the help of masculinizing or feminizing reconstruction and at determining the fate of the gonads. Currently, due to the high risk of developing tumors, surgeons resort to bilateral removal of the gonads in all patients with a female phenotype, but with a male karyotype.

Hormone therapy for patients with the female sex is carried out in order to prevent the manifestations of post-castration syndrome, which develops in patients who underwent removal of the gonads. Hormonal treatment consists of the use of only estradiol preparations - estrophema, proginova. In addition, it is possible to prescribe combined oral contraceptives, such as Mersilon, Novinet, Janine, Diane-35. For the correction of postmenopausal disorders, monophasic and biphasic hormone replacement therapy drugs are used. Endocrinologist consultation

Specialists of the North-West Endocrinology Center diagnose and treat diseases of the endocrine system. The center's endocrinologists in their work are based on the recommendations of the European Association of Endocrinologists and the American Association of Clinical Endocrinologists. Modern diagnostic and treatment technologies ensure optimal treatment results.

Pelvic ultrasound

Pelvic ultrasound - ultrasound examination of the pelvic organs (uterus, fallopian tubes, vagina, ovaries, bladder). Pelvic ultrasound can be performed to diagnose diseases of the female genital organs or the bladder, as well as to diagnose the condition of the fetus during pregnancy or to diagnose the pregnancy itself

Urologist-andrologist consultation

Andrology is a field of medicine that studies men, male anatomy and physiology, diseases of the male genital area and methods of their treatment. At the moment, there is no specialization in andrology in Russia, therefore, specialists wishing to engage in this field of medicine must receive basic education in urology, followed by additional specialization in endocrinology.

Pediatric endocrinologist consultation

Very often, patients under the age of 18 come to see the specialists of the North-West Endocrinology Center. Special doctors - pediatric endocrinologists work for them in the center.

Ultrasound of the scrotum and testicles

Ultrasound of the scrotum and testicles is one of the most effective methods of examining the male reproductive system, including the testes, spermatic cords and epididymis

The term "hermaphroditism syndrome" refers to a group of sexual differentiation disorders that accompany many congenital diseases and manifest themselves with rather diverse symptoms. Patients suffering from this pathology have signs of both men and women.

Below we will talk about why hermaphroditism occurs, what clinical manifestations it can be accompanied by, and also familiarize the reader with the principles of diagnosis and treatment of this pathology.

Allocate false hermaphroditism, when the structure of the genitals does not correspond to the sex of the gonads (gonads). In this case, the genetic sex is determined by the belonging of the gonads and is called male or female pseudohermaphroditism, respectively. If the elements of both the testicle and the ovary are determined in a person at the same time, this condition is called true hermaphroditism.

In the structure of urological and gynecological pathology, hermaphroditism is recorded in 2-6% of patients. Official statistics regarding this pathology are currently absent, but it is tacitly believed that hermaphroditism occurs more often than doctors register it. Such patients often hide under other diagnoses ("gonadal dysgenesis", "adrenogenital syndrome" and others), and also receive therapy in psychiatric departments, since their sexual dysfunctions are incorrectly regarded by doctors as diseases of the sexual centers of the brain.

Classification

Depending on the mechanism of development of hermaphroditism, there are 2 main forms: disorders of differentiation of the genitals (genitals) and disorders of differentiation of the sex glands, or gonads.

There are 2 types of genital differentiation disorders:

1. Female hermaphroditism (partial appearance of male sexual characteristics, the set of chromosomes is 46 XX):
   • congenital dysfunction of the adrenal cortex;
   • intrauterine fetal virilization under the influence of external factors (if the mother suffers from any tumor that produces male sex hormones - androgens, or takes drugs with androgenic activity).
2. Male hermaphroditism (inadequate formation of male sexual characteristics; the karyotype is as follows: 46 XY):
   • testicular feminization syndrome (tissues are sharply insensitive to androgens, which is why, despite the male genotype, and therefore the person's belonging to this sex, he looks like a woman);
   • lack of the enzyme 5-alpha reductase;
   • insufficient synthesis of testosterone.

Violations of the differentiation of the gonads are represented by the following forms of pathology:

• syndrome of bisexual gonads, or true hermaphroditism (the same person combines both male and female sex glands);
• Turner syndrome;
• pure agenesis of the gonads (complete absence of gonads in the patient, female genital organs, underdeveloped, secondary sexual characteristics are not determined);
• dysgenesis (violation of intrauterine development) of the testicles.

Causes of occurrence and mechanism of development of pathology

Both hereditary factors and factors affecting it from the outside can disrupt the normal development of the fetal genitals.

The causes of dysembryogenesis, as a rule, are:

• gene mutations in autosomes (non-sex chromosomes);
• pathology in the field of sex chromosomes, both quantitative and qualitative;
• external factors affecting the fetus through its mother at a certain period of development (the critical period in this situation is 8 weeks): tumors in the mother's body that produce male sex hormones, her intake of drugs with androgenic activity, exposure to radioactive radiation, various kinds of intoxication ...

Each of these factors can affect any of the stages of gender formation, as a result of which one or another complex of disorders characteristic of hermaphroditism develops.

Symptoms

Let's consider each of the forms of hermaphroditism in more detail.

Female pseudohermaphroditism

This pathology is associated with a defect in the enzyme 21- or 11-hydroxylase. It is inherited in an autosomal recessive manner (that is, not related to gender). The set of chromosomes in patients is female - 46 XX, the sex glands are also female (ovaries), formed correctly. The external genital organs are both male and female. The severity of these disorders depends on the severity of the mutation and varies from mild hypertrophy (increase in size) of the clitoris to the formation of external genitalia, which are almost similar to those of men.

Also, the disease is accompanied by severe disturbances in the level of electrolytes in the blood, which are associated with a deficiency of the hormone aldosterone. In addition, the patient may be found to have an increased blood volume and high blood sodium levels due to a deficiency of the enzyme 11-hydroxylase.

Male pseudohermaphroditism

As a rule, it manifests itself as androgenic insensitivity syndrome. The nature of inheritance is X-linked.

Due to a mutation in the androgen receptor gene, testicular feminization syndrome can develop. It is accompanied by the insensitivity of the man's body tissues to male sex hormones (androgens) and, on the contrary, their good sensitivity to female hormones (estrogens). This pathology is characterized by the following features:

• set of chromosomes 46 XY, but looks sick like a woman;
• aplasia (absence) of the vagina;
• insufficient hair for a man or complete absence of the latter;
• the development of the mammary glands characteristic of women;
• primary (although the genitals are developed according to the female type, they are absent);
• absence of a uterus.

In patients with this pathology, the male sex glands (testicles) are formed correctly, but they are not located in the scrotum (it is absent), but in the inguinal canals, the labia majora, in the abdominal cavity.

Depending on how much the patient's body tissues are insensitive to androgens, complete and incomplete forms of testicular feminization are emitted. There is a variety of this pathology, in which the patient's external genital organs look almost normal, close in appearance to those of healthy men. This condition is called Reifenstein syndrome.

Also, false male hermaphroditism can be a manifestation of impaired testosterone synthesis due to a deficiency of certain enzymes.

Disorders of the differentiation of the sex glands

Syndrome of pure gonadal agenesis

This pathology arises in connection with point mutations of the X- or Y-chromosome. Patients of normal growth, their secondary sexual characteristics are underdeveloped, there is sexual infantilism and primary amenorrhea (initially there is no menstruation).

The external genitals are usually female. In men, they sometimes develop in a masculine manner.

Turner syndrome

It is caused by a genetic mutation - monosomy (complete or partial) on the X chromosome. There are also abnormalities in the structure of this chromosome or mosaic variants of mutations.

As a result of such an anomaly, the processes of differentiation of the gonads and the function of the ovaries are disrupted. On both sides, there is a dysgenesis of the gonads, which are represented by streaks.

Genes for non-sex chromosomes are also affected. The growth processes of somatic cells and their differentiation are disrupted. Such patients are always short and have many different other anomalies (for example, a short neck, pterygoid folds of the neck, high palate, heart defects, kidney defects, and others).

Dysgenesis of the testicles (testicles)

There are 2 forms of it:

• bilateral (bilateral) - the testes are underdeveloped on both sides, do not produce normal sperm; karyotype - 46 XY, however, abnormalities in the structure of the X chromosome are determined; the internal genital organs are developed according to the female type, the external ones can have signs of both male and female; the testes do not produce testosterone, so the level of sex hormones in the patient's blood is sharply reduced;
• mixed - the sex glands are developed asymmetrically; on the one hand, they are represented by a normal testicle with preserved reproductive function, on the other, by a streak; in adolescence, some patients develop secondary sexual characteristics of the male type; when examining the chromosome set, as a rule, anomalies in the form of mosaicism are revealed.

True hermaphroditism

This pathology is also called bisexual gonad syndrome. This is a rare disease characterized by the presence of structural elements of both the testicle and the ovary in the same person. They can be formed separately from each other, but in some cases the so-called ovotestis is found in patients - the tissues of both sex glands in one organ.

The set of chromosomes in true hermaphroditism is usually normal female, but in some cases male. Sex chromosome mosaicism also occurs.

The symptomatology of this pathology is quite diverse and depends on the activity of the testicular or ovarian tissue. The external genitals are represented by both female and male elements.

Diagnostic principles

Ultrasound allows you to assess the condition of the gonads.

The process of making a diagnosis, as in other clinical situations, includes 4 stages:

• collection of complaints, anamnesis (history) of life and current illness;
• objective examination;
• laboratory diagnostics;
• instrumental diagnostics.

Let's dwell on each of them in more detail.

Complaints and anamnesis

Among other data, in case of suspicion of hermaphroditism, the following points are of particular importance:

• whether the patient's immediate family suffers from similar disorders;
• the fact of the removal operation in childhood (this and the previous paragraphs will push the doctor into thinking about the testicular feminization syndrome);
• features and growth rates in childhood and adolescence (if the growth rate in the first years of a child's life outpaced that of his peers, and at 9-10 years old stopped or slowed down sharply, the doctor should think about the diagnosis of adrenal cortex dysfunction, which arose against the background of an increased level of androgens in blood; this pathology can also be suspected in a child c).

Objective examination

The most important point here is the assessment of the patient's sexual development and physique. The detection, in addition to sexual infantilism, of growth disorders and minor anomalies in the development of other organs and systems makes it possible to diagnose Turner syndrome even before karyotyping.

If, on palpation of a man's testicles, they are determined in the inguinal canal or in the thickness of the labia majora, one can suspect male pseudohermaphroditism. The discovery of the absence of the uterus will convince the doctor even more of this diagnosis.

Laboratory diagnostics

The most informative method for diagnosing this pathology is karyotyping - a cytogenetic study of chromosomes - their number and structure.

Also, patients with suspected hermaphroditism are determined by the concentration in the blood of luteinizing and follicle-stimulating hormones, testosterone and estradiol, less often - mineral and glucocorticoids.

In difficult diagnostic situations, a test with hCG is performed.

Instrumental diagnostics methods

To assess the condition of the genitals, the patient is prescribed an ultrasound of the pelvic organs, and in some cases, a computed tomography of this area.

The most informative is the endoscopic examination of the internal genital organs and their biopsy.

Treatment principles

The main direction of treatment for hermaphroditism is surgery to correct the patient's sex. The latter chooses his gender, in accordance with this decision, the surgeons carry out the reconstruction of the external genitalia.

Also, in many clinical situations, such patients are recommended to undergo a bilateral gonadectomy - to completely remove the sex glands (testicles or ovaries).

For female patients, if hypogonadism is diagnosed, hormone therapy is prescribed. It is also indicated for patients who have had their gonads removed. In the latter case, the purpose of taking hormones is to prevent the development of post-castration syndrome (deficiency of sex hormones).

So, the following drugs can be prescribed to patients:

• estradiol (one of its trade names is Proginova, there are others);
• COCs (combined oral contraceptives) - Mersilon, Logest, Novinet, Yarina, Zhanin and others;
• drugs for hormone replacement therapy for disorders that have arisen after the onset (climodien, femoston, and so on);
• synthetic analogs of glucocorticoids and mineralocorticoids (depending on which hormone deficiency occurs in a particular patient); they are prescribed for adrenal dysfunction, which resulted in sexual dysfunction;
• to stimulate the growth of the patient, persons suffering from Turner syndrome are prescribed growth hormone preparations (Norditropin and others);
• testosterone (omnadren, sustanon) - it is recommended to use it for the purpose of hormone therapy for males.

Patients suffering from hermaphroditism, even after surgery, should be under the supervision of an endocrinologist. Also, many of them are shown consultations of a psychotherapist, sexologist or psychologist.

Self-fertilizing animals reproduce, other things being equal, twice as fast as dioecious. Why does dioeciousness prevail in nature? To answer this question, roundworm breeds were artificially bred. Caenorhabditis elegans, some of which practice only cross-fertilization, others only self-fertilization. Experiments with these worms have confirmed two hypotheses about the benefits of cross-fertilization. One advantage is a more effective purification of the gene pool from harmful mutations, the second is the accelerated accumulation of beneficial mutations, which helps the population to adapt to changing conditions.

Double the price of males

Why do we need sexual reproduction, why do we need males? The answers to these questions are not at all as obvious as they might seem.

Renowned evolutionist John Maynard Smith drew attention to the severity of this problem in his book The evolution of sex(1978). Maynard Smith examined in detail the paradox, which he gave the name "double cost of sex" (two-fold cost of sex). Its essence is that, all other things being equal, asexual reproduction (or self-fertilization) is exactly two times more effective than cross-fertilization with the participation of males (see figure). In other words, males are prohibitively expensive for the population. Abandoning them gives an immediate and very significant gain in the rate of reproduction. We know that, purely technically, the transition from dioeciousness and cross fertilization to asexual reproduction or self-fertilization is quite possible, there are a lot of examples in both plants and animals (see, for example: Females of the giant Komodo monitor reproduce without the participation of males, "Elements" , 26.12.2006). Nevertheless, asexual races and populations of self-fertilizing hermaphrodites for some reason have not yet supplanted those who reproduce in the "usual" way, with the participation of males.

Why are they still needed?

From what has been said, it follows that cross fertilization should provide some advantages, so significant that they overlap even the double gain in reproductive efficiency given by the rejection of males. Moreover, these advantages should appear immediately, and not sometime in a million years. Natural selection does not care about distant prospects.

There are many hypotheses about the nature of these benefits (see: Evolution of sexual reproduction). We'll look at two of them. The first is known as the "Müller ratchet." cannot get rid of it. It will be, like a generic curse, transmitted to all its descendants forever (unless a reverse mutation occurs, and the probability of this is very small.) In asexual organisms, selection can only reject whole genomes, but not individual genes. In a series of generations of asexual organisms (subject to certain conditions), a steady accumulation of harmful mutations can occur.One of these conditions is a sufficiently large genome size. , by the way, genomes are small compared to other animals. Maybe that's why they can afford self-fertilization (see below).

If organisms reproduce sexually and practice cross fertilization, then individual genomes are constantly scattered and mixed, and new genomes are formed from fragments that previously belonged to different organisms. As a result, a special new essence arises, which asexual organisms do not have - gene pool population. Genes get the ability to reproduce or be discarded independently of each other. A gene with an unsuccessful mutation can be rejected by selection, and the rest ("good") genes of a given parent organism can safely remain in the population.

Thus, the first idea is that sexual reproduction helps to cleanse genomes from the "genetic burden", that is, helps to get rid of constantly emerging harmful mutations, preventing degeneration (reducing the general fitness of the population).

The second idea is akin to the first: it assumes that sexual reproduction helps organisms more efficiently adapt to changing conditions due to the accelerated accumulation of mutations that are useful in a given environment. Let's say one individual has one beneficial mutation, another has another. If these organisms are asexual, they have little chance of waiting for both mutations to combine in the same genome. Sexual reproduction provides this opportunity. It actually makes all beneficial mutations that have arisen in the population "common property." It is clear that the rate of adaptation to changing conditions in organisms with sexual reproduction should be higher.

All of these theoretical constructs, however, are based on certain assumptions. The results of mathematical modeling indicate that the degree of usefulness or harmfulness of cross fertilization in comparison with asexual reproduction or self-fertilization depends on a number of parameters. These include population size; mutation rate; genome size; quantitative distribution of mutations depending on the degree of their harmfulness / usefulness; the number of offspring produced by one female; selection efficiency (the degree of dependence of the number of offspring left not on random, but on genetic factors), etc. Some of these parameters are very difficult to measure not only in natural, but also in laboratory populations.

Therefore, all hypotheses of this kind are in dire need not so much of theoretical substantiations and mathematical models (all of this is already in abundance), but of direct experimental verification. However, not so many similar experiments have been carried out so far (Colegrave, 2002. Sex releases the speed limit on evolution // Nature... V. 420. P. 664-666; Goddard et al., 2005. Sex increases the efficacy of natural selection in experimental yeast populations // Nature... V. 434. P. 636-640). New study by University of Oregon biologists on roundworm Caenorhabditis elegans, vividly illustrated the effectiveness of both considered mechanisms, providing an advantage to those populations that do not abandon males, despite their "double price".

Unique object for studying the role of males

Worms Caenorhabditis elegans as if deliberately created for the experimental verification of the above hypotheses. These worms have no females. The populations are composed of males and hermaphrodites, the latter being numerically predominant. Hermaphrodites have two X chromosomes, males have only one (the X0 sex determination system, like in Drosophila). Hermaphrodites produce sperm and eggs and can reproduce unaided by self-fertilization. Males only produce sperm and can fertilize hermaphrodites. As a result of self-fertilization, only hermaphrodites are born. With cross fertilization, half of the offspring are hermaphrodites, half are males. Usually the frequency of cross fertilization in populations C. elegans does not exceed a few percent. To determine this frequency, it is not necessary to observe the intimate life of worms - it is enough to know the percentage of males in the population.

It should be clarified that self-fertilization is not exactly the same as asexual (clonal) reproduction, however, the differences between them quickly disappear in a series of self-fertilizing generations. Self-fertilizing organisms become homozygous at all loci over several generations. After that, the offspring ceases to differ genetically from their parents, just like in clonal reproduction.

Have C. elegans mutations are known that affect the frequency of cross fertilization. One of them, xol-1, is fatal for males and actually leads to the fact that only hermaphrodites, which reproduce by self-fertilization, remain in the population. Another, fog-2, deprives hermaphrodites of the ability to produce sperm and actually turns them into females. A population in which all individuals carry this mutation becomes a normal dioecious population, like most animals.

The authors, using classical techniques (by crossing, not genetic engineering), bred two pairs of worm breeds with almost identical genomes, differing only in the presence of mutations xol-1 and fog-2... The first breed in each pair, with a mutation xol-1, reproduces only by self-fertilization (obligate selfing, OS). Second, with a mutation fog-2, can reproduce only by obligate outcrossing (OO). Each pair of breeds was accompanied by a third, with the same genetic "background", but devoid of both mutations (wild type, WT). In WT breeds, the cross-fertilization rate under standard laboratory conditions does not exceed 5%.

Males are needed! Tested experimentally

Two series of experiments were carried out with these triplets of rocks.

In the first episode tested the hypothesis that cross fertilization helps to get rid of the "genetic burden". The experiment lasted for 50 generations (worms, of course, not experimenters). Each generation of worms has been exposed to a chemical mutagen called ethyl methanesulfonate. This resulted in an approximately fourfold increase in the mutation frequency. Young animals were placed in a Petri dish, divided in half by a vermiculite wall (see figure), and the worms were planted in one half of the dish, and their food was bacteria E. coli- was in the other half. During transplantation, the worms were treated with an antibiotic to cleanse the accidentally adhered bacteria. As a result, in order to get to food, which means to get a chance to survive and leave offspring, the worms had to overcome the obstacle. Thus, the experimenters increased the efficiency of "cleansing" selection, which weeds out harmful mutations. Under normal laboratory conditions, selection efficiency is very low because the worms are surrounded by food on all sides. In such a situation, even very weak animals overloaded with harmful mutations can survive and reproduce. In the new experimental setup, this leveling was brought to an end. To crawl over the wall, the worm must be healthy and strong.

The authors compared fitness in worms before and after the experiment, that is, in individuals of the first and fiftieth generation. Worms C. elegans can be stored frozen for a long time. This greatly facilitates such experiments. While the experiment lasted, a sample of the 1st generation worms lay quietly in the freezer. Fitness was measured as follows. The worms were mixed in equal proportions with control worms, into the genome of which the gene for the luminous protein had been inserted, and planted in the experimental setup. The animals were given time to overcome the barrier and reproduce, and then the percentage of non-luminous individuals in the offspring was determined. If this percentage has increased in the fiftieth generation compared to the first, it means that during the experiment the fitness has increased, if it has decreased, then there has been a degeneration.

The results of the experiment are shown in the figure. They clearly show that cross-fertilization is a powerful means of combating genetic burden. The higher the cross-fertilization rate, the better the final result (all lines in the figure increase from left to right). An artificially increased mutation rate led to the degeneration (decreased fitness) of all breeds of worms, except for OO - "obligate cross-hairs".

Even for those breeds in which mutagenesis was not artificially accelerated, the high rate of cross fertilization gave an advantage. Under normal laboratory conditions, this advantage does not appear because the worms do not need to climb over the walls to get to the food.

It is curious that in one of the two control OS breeds (“obligate self-fertilizers”), even without increasing the mutation rate, the refusal of cross fertilization led to degeneration (the left square in the upper pair of curves in the figure is below zero).

The figure also shows that the cross-fertilization rate in most wild breeds (WT) during the experiment was significantly higher than the original 5%. This is perhaps the most important result. It means that under harsh conditions (meaning both the need to climb over the barrier and the increased rate of mutagenesis), natural selection gives a clear advantage to individuals that reproduce by cross fertilization. The offspring of such individuals turns out to be more viable, and therefore, during the experiment, selection is made for the tendency to cross fertilization.

Thus, the first experiment convincingly confirmed the hypothesis that cross fertilization helps the population to get rid of harmful mutations.

In the second episode experiments tested whether cross-fertilization helps to develop new adaptations by accumulating beneficial mutations. This time, the worms had to overcome an area inhabited by pathogenic bacteria to get to food. Serratia... These bacteria enter the digestive tract C. elegans, cause a dangerous disease in the worm, which can end in death. To survive in this situation, the worms had to either learn not to swallow harmful bacteria, or develop resistance to them. It is not known which of the variants the experimental populations of worms chose, but over 40 generations the OO breeds have perfectly adapted to the new conditions, the WT breeds have adapted somewhat worse, and the OS breeds have not adapted at all (their survival rate in the environment with harmful bacteria remained at the initial low level). And again, in the course of the experiment, in WT breeds, the frequency of cross fertilization increased sharply under the influence of selection.

Thus, cross fertilization really helps the population to adapt to changing conditions, in this case, to the emergence of a pathogenic microbe. The fact that the WT breeds experienced an increased rate of cross-fertilization during the experiment means that mating with males (as opposed to self-fertilization) gives hermaphrodites an immediate adaptive advantage, which apparently outweighs the "double price" they have to pay to produce males.

It should be noted that cross-fertilization occurs not only in dioecious organisms. For example, many invertebrates are hermaphrodites, fertilizing not themselves, but each other - crosswise. In plants, cross-pollination of bisexual ("hermaphrodite") individuals is also, to put it mildly, not uncommon. Both hypotheses tested in this work are quite applicable to such hermaphrodites. In other words, this work did not prove that "cross hermaphroditism" is in any way inferior to dioeciousness. And you don't have to pay the notorious "double price" for the first of these two options. Therefore, the problem still remains.

Experiments have revealed the disadvantages of self-fertilization versus cross-fertilization, but they did not explain why many organisms preferred dioeciousness to “cross-hermaphroditism”. The key to solving this conundrum is most likely sexual selection. Dividing cavities enable females to pick their mates meticulously, and this can serve as an additional way to increase the efficiency of rejection of harmful and accumulation of beneficial mutations. Perhaps this hypothesis will someday receive experimental confirmation.

Hermaphroditism (named after the Greek god Hermaphrodite, Greek ρμαφρόδιτος) is the simultaneous or sequential presence of male and female sexual characteristics and reproductive organs in the body.

Distinguish between natural hermaphroditism inherent in various species of animals and plants (monoeciousness) and abnormal (pathological) hermaphroditism of normally dioecious animals (see Gynandromorphism, Intersexuality).

Hermaphroditism is quite widespread in nature - both in the plant kingdom (in this case, the terms monoecious or polyhomous are usually used), and among animals. Most of the higher plants are hermaphrodites, in animals hermaphroditism is widespread primarily among invertebrates - a number of intestinal cavities, the vast majority of flat, some annelids and round worms, molluscs, crustaceans (in particular, most species of barnacles) and insects (coccids).

Among vertebrates, many species of fish are hermaphrodites, and hermaphroditism is most common in fish inhabiting coral reefs.

With natural hermaphroditism, an individual is capable of producing both male and female gametes, while a situation is possible when both types of gametes (functional hermaphroditism), or only one type of gametes (afunctional hermaphroditism) have the ability to fertilize.

With synchronous hermaphroditism, the individual is capable of simultaneously producing both male and female gametes.

In the plant kingdom, this situation often leads to self-fertilization, which occurs in many species of fungi, algae and flowering plants (self-pollination in self-fertile plants).

In the animal kingdom, self-fertilization with synchronous hermaphroditism occurs in helminths, hydras and molluscs, as well as some fish (Rivulus marmoratus); however, in most cases, autogamy is prevented by the structure of the genital organs, in which the transfer of one's own spermatozoa to the female genital organs of an individual is physically impossible (molluscs, in particular , alysia, ciliary worms), or the impossibility of merging their own differentiated gametes into a viable zygote (some ascidians).

Accordingly, with exogamous synchronous hermaphroditism, two types of copulatory behavior are observed:

mutual fertilization, in which both copulating individuals play the role of both males and females (most often among invertebrates, earthworms, grape snails can be cited as an example)

sequential fertilization - one of the individuals plays the role of a male, and the other is a female; in this case, mutual fertilization does not occur (for example, in perch fish of the genera Hypoplectrus and Serranus).

In the case of sequential hermaphroditism (dichogamy), the individual sequentially produces male or female gametes, while either sequential activation of the male and female gonads occurs, or a change in the phenotype associated with sex as a whole. Dichogamy can manifest itself both within one reproductive cycle and during the life cycle of an individual, while the reproductive cycle can begin either from the male (protandria) or from the female (protogyny).

In plants, as a rule, the first option is widespread - during the formation of flowers, the anthers and stigmas do not ripen at the same time. Thus, on the one hand, self-pollination is prevented and, on the other hand, due to the non-simultaneous flowering time of different plants in the population, cross-pollination is ensured.

In the case of animals, a phenotype change occurs most often, that is, a sex change. A striking example is many fish species - representatives of the families of wrasse (Labridae), groupers (Serranidae), pomacentridae (Pomacentridae), parrot fish (Scaridae), most of which are inhabitants of coral reefs.

Pathological hermaphroditism is observed in all groups of the animal world, including higher vertebrates and humans. Hermaphroditism in humans is a pathology of sexual determination at the genetic or hormonal levels.

Distinguish between true and false hermaphroditism:

True (gonadal) hermaphroditism is characterized by the simultaneous presence of male and female genital organs, along with this there are both male and female genital glands. The testicles and ovaries with true hermaphroditism can either be combined into one mixed sex gland, or are located separately. Secondary sexual characteristics have elements of both sexes: low timbre of voice, mixed (bisexual) type of figure, to some extent developed mammary glands.

The chromosome set (karyotype) in such patients usually corresponds to the female karyotype. In more rare cases, there is a situation when there are both cells containing a female chromosome set and cells containing a male chromosome set (the phenomenon of so-called mosaicism). True hermaphroditism is an extremely rare disease (only about 150 cases are described in the world literature).

False hermaphroditism (pseudohermaphroditism) occurs when there is a contradiction between the internal (chromosomal and gonadal) and external (structure of the genital organs) signs of sex (bisexual development), i.e. the sex glands are formed correctly according to the male or female type, but the external genital organs have signs of bisexuality.

Gynandromorphism (ancient Greek γυνή - woman + ἀνήρ, genus ἀνδρός - man + μορφή - type, form) is an anomaly, expressed in the fact that in one organism large areas of the body have a genotype and signs of different sexes. It is the result of the presence in the male and female cells of the body of sets of sex chromosomes with different numbers of the latter, such as in many insects. Gynandromorphism occurs as a result of an incorrect distribution of sex chromosomes among cells during the impaired maturation of the egg, its fertilization or cleavage.

Individuals - gynandromorphs are most pronounced in insects with clearly manifested signs of sexual dimorphism, while the following types of gynandromorphs are morphologically distinguished:

bilateral, in which one longitudinal half of the body has the characteristics of a male, the other is female;

anteroposterior, in which the front part of the body bears signs of one sex, and the back part of the other;

mosaic, in which parts of the body are interspersed, bearing signs of different sexes.

In vertebrates and in humans, due to the action of sex hormones, such phenomena lead to sexual anomalies, in which the sectorial distribution of male and female tissues is usually less pronounced.

With intersexuality, there is a more complex differentiation of female and male characteristics.

Intersexuality is the presence of signs of both sexes in a dioecious organism, and these signs are not fully developed, intermediate (cf. Hermaphroditism). Signs of both sexes appear together on the same parts of the body (cf. Gynandromorphism).

The embryonic development of such an organism is called intersex, it starts normally, but from a certain point it continues like the other sex. The earlier the direction of the organism's development changes, the more pronounced its intersexuality is.

It is the result of a deviation from the norm in the set of sex chromosomes and genes at the time of fertilization when the gametes are joined into a zygote. The nature of the disorder is triploid or otherwise - aneuploid intersection. Diploid intersexuality is observed when crossing different geographical races in a gypsy moth, either in females or in males, depending on the type of crossing.

Forms of intersexuality, the so-called pseudohermaphroditism in humans, can also be caused by a violation of the normal number of sex chromosomes. At the same time, in Drosophila flies, the determining factor in the development of sex is the ratio of the number of pairs of sex chromosomes and autosomes, therefore, intersexuality in them is usually associated with a violation of this ratio (for example, it is observed with a ratio of 3A: 2X - three sets of autosomes per two sex chromosomes). In humans, the determining factor in the development of the male sex is the presence of the Y-chromosome, while traits of intersexuality are observed in men with Klinefelter's syndrome (set of sex chromosomes XXY).

Hormone intersexuality. If in animals the secretion of male or female hormones by the sex glands determines the development of secondary sexual characteristics, then the phenomenon of hormonal intersexuality can be observed in them.

Ticket 13

1. Provisional organs, types and formation of formations of provisional cells

Provisional organs (German provisorisch - preliminary, temporary) are temporary organs of the embryos of the iliums of multicellular animals, functioning only during the embryonic or larval period of development. They can perform functions specific to the embryo or larva, or the basic functions of the body before the formation of similar definitive (final) organs characteristic of the adult body.

Examples of provisional organs: chorion, amnion, yolk sac, allantois and serous membrane, and others.

The amnion is a temporary organ that provides an aquatic environment for the development of the embryo. In human embryogenesis, it appears at the second stage of gastrulation, first as a small vesicle, the bottom of which is the primary ectoderm (epiblast) of the embryo

The amniotic membrane forms the wall of a reservoir filled with amniotic fluid that contains the fetus.

The main function of the amniotic membrane is the production of amniotic fluid, which provides an environment for the developing organism and protects it from mechanical damage. The epithelium of the amnion, facing its cavity, not only secretes amniotic fluid, but also takes part in their reabsorption. In the amniotic fluid, the required composition and concentration of salts are maintained until the end of pregnancy. Amnion also performs a protective function, preventing harmful agents from entering the fetus.

The yolk sac is an organ that stores nutrients (yolk) necessary for the development of the embryo. In humans, it is formed by the extraembryonic endoderm and the extraembryonic mesoderm (mesenchyme). The yolk sac is the first organ in the wall of which blood islets develop, forming the first blood cells and the first blood vessels that provide oxygen and nutrients to the fetus.

Allantois is a small process in the section of the embryo that grows into the amniotic leg. It is a derivative of the yolk sac and consists of an extraembryonic endoderm and a visceral mesoderm. In humans, allantois does not achieve significant development, but its role in providing nutrition and respiration of the embryo is still great, since vessels located in the umbilical cord grow along it to the chorion.

The umbilical cord is an elastic cord that connects the embryo (fetus) to the placenta.

Further development of the chorion is associated with two processes - the destruction of the uterine mucosa due to the proteolytic activity of the outer layer and the development of the placenta.

The placenta (child's place) of a person belongs to the type of discoidal hemochorial villous placentas. The placenta provides a connection between the fetus and the mother's body, creates a barrier between the blood of the mother and the fetus.

Placenta functions: respiratory; transport of nutrients, water, electrolytes; excretory; endocrine; participation in the reduction of the myometrium.

S. Afonkin

Why aren't we hermaphrodites?

Looking for a suitable gift for March 8 or, with a light sigh, fulfilling some feminine whim, you sometimes ponder over a seemingly strange question: why did Mother Nature deign to divide the human race into halves separately existing in space into female and male sex? We are so accustomed to this division that we perceive it almost as the only possible one.

Indeed, the animals, birds and fish around us, not to mention most other, more primitive creatures, are also dioecious. But some show us a completely different and seemingly much more reasonable solution. Both the female and male reproductive systems coexist peacefully in one body. Biologists called this phenomenon hermaphroditism.

Legend says that Hermaphrodite was the name of the son of Hermes and Aphrodite, The nymph Salmakis fell in love with a beautiful young man, but he did not reciprocate. Offended by the inattention, the nymph filed a complaint with a higher authority to Aphrodite herself, the mother of Hermaphrodite. And since she held the position of the goddess of love on Olympus and was obliged to indulge the lovers, then without thinking twice, with the determination characteristic of the gods, she merged the nymph and Hermaphrodite into a single being so that the latter would not run away from the girl.

Hermaphroditism in humans is extremely rare as a pathology at the genetic or hormonal levels. Among animals, however, there are species for which hermaphroditism is the norm. This is how, for example, some crustaceans and many worms are arranged.

A skeptic who is familiar with biology may notice that self-fertilization possible with hermaphroditism is fraught with the accumulation and manifestation of genetic errors. Indeed, one of the tasks of the sexual reproduction method is to mix well, to shuffle the genetic material of the parents, which, in turn, increases the diversity of offspring and prevents the manifestation of defects in genes. So two books with the same text, published in different publishers and in different years, are unlikely to have the same typos, and if you read them at the same time, you can restore the original text without distortion. Exactly the same correction occurs when any pair of chromosomes work together, one of which comes from the father, and the other from the mother. Remember the long practice of politically advantageous dynastic marriages between close relatives often undermined the health of the reigning families. What can we say about self-fertilization in the most closely related marriage imaginable!

This is all true. However, in true hermaphrodites, it rarely comes to self-fertilization. Most often, each such creature acts in turn in the role of a male, then in the role of a female. If it were possible for people, the problems of emancipation, sexism of any discrimination caused by one or another sexual orientation and belonging to a particular gender would disappear. What kind of discrimination is there when hiring, if the best foreman of the workshop Sidorov can go on maternity leave at any time! Probably, family problems would be solved easier if partners regularly changed roles. And in the case of divorces of androgynous married couples, the children would simply be given to the one of the spouses who gave birth to them. In extreme circumstances, self-fertilization can be used. For example, Robinson Crusoe would not be sad alone on a desert island, but would live with his family.

Needless to say, the benefits of hermaphroditism can seem tempting and even somewhat beneficial. However, with rare exceptions, all vertebrates are clearly divided into males and females, and we, humans, into men and women. What's the matter? Why is dioeciousness more profitable and evolutionarily attractive than hermaphroditism, in addition to the already mentioned genetic benefit?

In order to provide a theoretical basis for the phenomenon of heterosexuality, Doctor of Biological Sciences Vigen Artavazdovich Geodakyan created his own evolutionary theory of sex, which he has been fruitfully developing for a long time. Its essence boils down to the following.

Any system striving for self-preservation (for example, a biological species), which is in an unstable environment that changes over time, tries to isolate itself from this environment and, ideally, become completely independent of the surrounding conditions. The entire evolution of life on Earth is a long way of struggle for independence from the whims of the environment. A long way has been passed from the Cambrian jellyfish drying out at low tide to the modern man with his air conditioners and spacesuits.

In order to achieve such impressive success, living things constantly had to solve two conflicting tasks. On the one hand, to store and transmit in time already established information about your own device. On the other hand, constantly react to its changes, adapt to its changing properties, look for ways to counteract it and, ultimately, introduce appropriate adjustments in the information transmitted along the chain of generations. For where can one get away from her, the environment?

At the dawn of evolution, probably even during the reign of unicellular organisms, the solution of these different strategic tasks was entrusted to two opposite sexes, because giving two conflicting orders to one subordinate is stupid and ineffective. The female sex took upon itself the function of saving and transmitting, while the male sex took on the function of exploring and making changes to the stored. Figuratively speaking, the female sex has taken on a conservative role, and the male gender has taken on a revolutionary one.

Before the advent of technology, there was only one way to assess the habitat at the cost of your life. You fit the habitat, live and be fruitful. Sorry ... In order to better fulfill its mission, the male gender has acquired a number of interesting properties. In males, the frequency of mutations of a kind of random samples is higher according to the principle: "What happens if you do this?" In males, all genetically determined traits are more clearly and unambiguously manifested. In humans, this phenomenon makes identical twins boys look more alike than twins girls.

On the other hand, the phenotypic diversity of all males as a whole is greater than that of females, again, to make life easier to choose among them. For example, the frequency of early infant mortality is higher in boys, but on the other hand, there are more men than women among centenarians. Wednesday had plenty to choose from.

Men are more likely to ask for trouble, they have higher search activity and aggressiveness. Accident? Not at all! It is this behavior that guarantees a high-quality “shooting” of poorly adapted individuals by the environment. The average life expectancy for men is shorter than that of women. Accident? No, the result of the terrible pressure of the environment on non-plastic men! The real life span of men is almost always less than nature allotted to them. Likewise, the average sparrow lives free for less than a year, and quietly chirps in a cage for two decades. What sparrows will live free until the second year and finally have a family? Shootable, but unfinished by the habitat.

If the water, fire and copper pipes of the environment have been successfully passed, if the environment has put its OTK stamp on a given genotype, its carrier has every chance to actively spread his genes in the next generation, becoming the owner of a numerous harem or, at worst, just a father with many children. Have you ever wondered why nature has created such an inequality between the sexes in the ability to leave offspring? The female sex is limited here. How many children can a woman give birth to in her entire life? At best, three dozen? A padishah or a popular singer? Here the count can go to thousands, if not tens of thousands of descendants.

A similar imbalance, only in the ratio of gamete sex cells, arose in the world of unicellular organisms. Even in the Cambrian ocean, one regally huge female gamete of algae or some jellyfish was surrounded by a whole crowd of male gametes. For reproductive success, each of these gentlemen had to perform truly Herculean feats: spend a lot of energy for a long journey, swim a huge (from a cellular point of view) distance, find the desired cell by smell and merge with it before others. In fact, we observe the same picture during fertilization in most modern creatures.

Biologists talk about gametic selection that occurs before fertilization. As a result of the intrauterine marathon, the overwhelming majority of male spermatozoa leave the race and simply do not get to the egg. Are their vital abilities tested at this stage? Quite possibly. It is said that due to the effect of gametic selection, the frequency of genetic disorders in the offspring of people who survived the bombing of Hiroshima was much lower than predicted.

Female representatives are more plastic. This makes it possible to deftly escape from the pressure of the environment, to preserve the inherited set of genes, regardless of what was inherited. In other words, to adapt to any life situation, explicitly or subconsciously thinking about only one thing about children. About the possibility and necessity of passing on the genetic baton to them.

In a stable environment, the difference between male and female sex is reduced to purely anatomical differences in the reproductive organs. In other words, sexual dimorphism is minimized. However, as soon as the environment begins to change, the gender divergence immediately begins in a number of features that can have an adaptive meaning. First, the male sex begins to change at the cost of his life, he goes through the possible answers to the changed conditions. Then, after the selection of the most acceptable options, the "cautious" female sex begins to follow. In other words, any trait that is differently expressed in the two sexes changes over time from its feminine form to its masculine.

Looking at sexual dimorphism from this angle, one can clearly see the direction of evolutionary change in a species or a whole group of species. For example, in most vertebrates, males are larger than females. Consequently, the evolution of this group follows the path of a gradual increase in the average body size. Take a look at the graph of the average height of people over the past several thousand years, and you will understand why men are on average slightly taller than women.

The futuristic, forward-looking nature of the changes inherent in the male sex is clearly manifested in the nature of congenital pathologies. In females, these anomalies are of an atavistic nature, that is, they remind of the stages of evolution that have already passed. In the male sex, they are directed towards the future, that is, they seem to continue the vector of already outlined changes. For example, among newborns with three kidneys, there are twice as many girls as boys, and vice versa, among newborns with one kidney, boys predominate. The picture is the same in the case of an anomalous number of ribs. In full accordance with the Old Testament, boys with fewer of them are born more often than girls. Why is that? It's that simple! The evolution of all chordates followed the path of decreasing the number of homologous organs (including kidneys and ribs). Both sexes show echoes of this process in different ways. The female shows what was, the male shows what will be.