Surely each of you knows the story described in the Holy Scriptures. Mary, being God's chosen one, brought into the world an immaculately conceived child. Whether this actually happened or was just the result of the wild imagination of the authors of those times is difficult to say today. But let it be known to you that the virgin birth is quite common in our world. What is parthenogenesis and what is its essence?

Amazing world

Perhaps one of the greatest mysteries of our universe is the origin of life. Where it came from and who is the creator of everything is a sealed mystery. But whoever our creator was, he did a great job of ensuring that life on the blue planet never runs out. Its various forms inhabiting the Earth are capable of reproducing their own kind in a wide variety of, sometimes very unexpected, ways.

Parthenogenesis

What is parthenogenesis? This is the ability of a female to give birth to a new generation without the participation of a sexual partner - a male. This does not mean that males are not needed at all; they are, of course, important. Parthenogenesis is not a method of asexual reproduction, as in some plants (budding, for example). But if it happens that a female for some reason could not find a partner for mating and fertilization of the egg did not occur, she will still be able to produce full-fledged offspring without his participation. This ability provides the species with very good survival. When numbers fall, females can replenish the population within a short time and continue the race. This is the essence of parthenogenesis.

Another important feature of such reproduction is the regulation of the ratio of the number of females and males. So, for example, in bees, drones (males) emerge from unfertilized eggs, and from fertilized eggs, workers emerge, which are all female.

Types of parthenogenesis

What is parthenogenesis and how can it occur in certain animals? In some species it is considered the main method of reproduction (obligate). For other forms, it is cyclical, that is, periodically offspring appear from unfertilized eggs, but more often with the participation of a male. The facultative, or emergency method of reproduction provides the species with survival in the most difficult living conditions; this is the essence of parthenogenesis for them. These cases are rather an exception, because usually such animals adhere to bisexual reproduction.

Parthenogenesis in animals

What is parthenogenesis? This is the process in which the parent egg, being unfertilized, begins to develop in order to subsequently turn into an adult full-fledged living being. Parthenogenesis can vary significantly between species. So, for example, reproduction by parthenogenesis in bees is significantly different from the reproduction of other insects, say, ants.

Knowledge of what parthenogenesis is and how it occurs has significantly influenced the development of science and given impetus to the emergence of certain trends in the industry. Thus, scientists learned that in the silkworm, parthenogenesis starts after exposure to certain temperatures. This significantly accelerated the breeding process of these insects.

The essence of parthenogenesis is well known to beekeepers and silk producers; many invertebrates use just this method. Some species of lizards and fish often practice this; the process is well known to representatives of the plant world; there are even parthenogenetic turkeys.

Representatives of science are working tirelessly to study this feature. Many attempts have been made to induce parthenogenesis in warm-blooded animals. Unfortunately, it is impossible to give examples, since in some cases cell growth and embryo development occurred, but the matter never reached the final stage. There is also considerable interest from the medical side. A survey was conducted, after which it became known that the majority of married couples who cannot have a baby would happily decide on such an immaculate conception. Who knows, maybe over time the veil of secrecy will be lifted. And a miracle will come true - parthenogenesis will be able to give life to a human baby.

On the eve of the Christian holiday of Easter, I would like to consider a topic that scientifically approaches one New Testament miracle.

According to legend, the Blessed Virgin Mary, without any fertilization, became pregnant and gave birth to the King of the Jews Jesus Christ - the Messiah, whose coming was predicted in the Old Testament.

“Without fertilization? Impossible!" – some will object. But such a phenomenon is possible. The Virgin Mary is called "Agni Parthene" in Greek, translated as "Pure Virgin".

Here from the word “ parthenay"- maiden, virgin - the term parthenogenesis was formed.

Reproduction by parthenogenesis

Parthenogenesis- This is the process by which reproduction occurs from unfertilized.

But this should not be confused with reproduction.

Reproduction by parthenogenesis- This is a form of sexual reproduction, as female gametes are formed.

One of the first to study parthenogenesis was the Swedish naturalist Charles Bonnet and German zoologist Karl Siebold.

Parthenogenesis is divided into two types: meiotic And ameiotic .

At ameiotic parthenogenesis the eggs remain diploid because they do not undergo meiosis.

At meiotic parthenogenesis the organism develops either from haploid egg, and is itself haploid, or egg restores diploidity and the organism becomes diploid.

Restoration of diploidity can occur in different ways: the egg can fuse with a polar body (this is similar to gamete copulation) or it can occur endomitosis.

Endomitosis – doubling process. As with, but the nuclear membrane does not dissolve and the cell does not divide.

What organisms can reproduce by parthenogenesis?

Here are some classic examples

Aphids. In this way, they quickly increase their numbers without much expense. Parthenogenetically breed in summer. The result is only females. This is a kind of preparation for unfavorable conditions, aimed at ensuring that as many individuals as possible survive. As autumn approaches, a different type of gamete is born, from which both males and females can emerge. And insects begin to reproduce through ordinary sexual intercourse.

Daphnia. During the summer they reproduce by ameiotic parthenogenesis. When the temperature of the reservoir drops and daylight hours shorten, haploid males appear. The population switches to ordinary sexual reproduction.

Rotifers. Don't be surprised if this name is not familiar to you; as far as I know, they are not in the school curriculum. In short: rotifers are a whole separate type. They are multicellular organisms, but their sizes are very small. Rotifers, like aphids and daphnia, reproduce by parthenogenesis in favorable conditions, and when unfavorable conditions occur, they switch to ordinary sexual reproduction. There are even some species such as rotifers that have achieved “perfection”: these species are formed only by females that reproduce by parthenogenesis. In such cases, when parthenogenesis is the only method of reproduction, it is called obligate. And when there is an alternation of parthenogenesis and another method of reproduction, parthenogenesis is called cyclical(like daphnia and aphids).

Bees. In bees, egg development follows two patterns: some are fertilized, some are not. From unfertilized eggs (1n), males develop - drones. Therefore, the somatic cells of drones are haploid ( You shouldn’t forget about this if you suddenly come across something on this topic in a problem on genetics).

From fertilized eggs, females develop - worker bees or a queen. In this case, when eggs can develop both as a result of fertilization and parthenogenetically, parthenogenesis is called facultative.

Thanks to the ability for facultative parthenogenesis in bees, the number of individuals of each caste (workers, drones) is controlled.

Rod Rock includes several species capable of parthenogenesis. Before the germ cells of these lizards undergo a mitotic increase in the number of chromosomes, therefore, after a normal meiotic cycle, the eggs become diploid and are ready to form a new organism. Rock lizards live on rocks and sometimes moving from one to another is problematic; in such conditions, parthenogenesis is precisely what is needed.

Parthenogenesis has been discovered in komodo dragons. Females have sex chromosomes: ZW, and males: ZZ. Therefore, as a result of parthenogenesis, organisms should be obtained: ZZ or WW, but WW are not viable. Therefore, in Komodo dragons, only males can develop as a result of parthenogenesis.

Parthenogenesis is also called virgin reproduction; this process is characteristic of species in which a short life cycle is accompanied by pronounced seasonal changes.

Androgenesis and gynogenesis

During the process of adrogenesis, the female germ cell does not take part in the development of a new organism, which appears as a result of the fusion of two nuclei of male germ cells - sperm. In this case, only males are present in the offspring. In nature, androgenesis occurs in hymenopteran insects.

During gynogenesis, the sperm nucleus does not merge with the egg nucleus; it can only stimulate its development, so-called false fertilization occurs. This process is characteristic of bony fish and roundworms, and the offspring consists only of females.

Haploid and diploid parthenogenesis

In haploid parthenogenesis, an organism develops from a haploid egg, and individuals can be female, male, or both, depending on the chromosomal sex determination of the species. In ants, bees and wasps, as a result of parthenogenesis, males emerge from unfertilized eggs, and females from fertilized eggs. Thanks to this, organisms are divided into castes; the process allows you to regulate the number of descendants of a certain type.

In some lizards, aphids and rotifers, diploid parthenogenesis is observed; it is also called somatic. In this case, diploid eggs are formed in females. This process makes it possible to maintain the number of individuals if the meeting of individuals of different sexes is difficult.

Natural and artificial parthenogenesis

Parthenogenesis is cyclical in rotifers, aphids and daphnia. In the summer, only females exist; they develop parthenogenetically, and in the fall, reproduction occurs with fertilization.

Parthenogenesis can be caused artificially, for example, by irritating the surface of silkworm eggs, heating or exposure to various acids; egg fragmentation can be achieved without fertilization. It was possible to obtain adult rabbits and frogs parthenogenetically.

Recently, scientists from the Institute for the Development of Cell Technology (Massachusetts USA) obtained full-fledged embryos from unfertilized eggs from 4 of 28 test macaques. They were able to achieve such results thanks to a chemical drug under the influence of which a special method of reproduction occurs - “parthenogenesis”. What is parthenogenesis?

Parthenogenesis(Parthenogenesis - from the Greek parthenos - girl, virgin + genesis - generation) - a form of sexual reproduction in which the development of an organism occurs from a female reproductive cell (egg) without fertilization by a male one (sperm).

Parthenogenesis should be distinguished from asexual reproduction when development occurs not from germ cells, but from somatic cells or organs by division, budding.

It's sexual, but same-sex reproduction, which arose during the evolution of organisms in dioecious forms. In cases where parthenogenetic species are represented only by females, one of the main biological advantages of parthenogenesis is the acceleration of the rate of reproduction of the species, since all individuals of such species are capable of leaving offspring. If a female develops from fertilized eggs, and a male from unfertilized eggs, parthenogenesis contributes to the regulation of numbers and sex ratios(for example, in bees, males - drones - develop parthenogenetically, and from fertilized ones - females - queens and worker bees).

Parthenogenesis - natural a normal method of reproduction for some species of animals and plants. Complete natural parthenogenesis occurs in invertebrate animals of all types, but most often in arthropods. Of the vertebrates, these are fish, some species of amphibians, reptiles, and certain species of birds (turkeys) reproduce parthenogenetically. In mammals, only cases of embryonic parthenogenesis are known; isolated cases of full development were observed in the rabbit during artificial parthenogenesis. In humans there are known cases when, under the influence of stressful situations of high temperatures and in other extreme situations, a female egg can begin to divide, even if it is not fertilized, but in 99.9% of cases it soon dies (according to some data, 16 cases of immaculate conception that took place in history are known in history Africa and European countries).

Parthenogenesis may be obligate, when the eggs are only capable of parthenogenetic development, and optional in which eggs can develop both through parthenogenesis and as a result of fertilization (in bees). Often reproduction through parthenogenesis alternates with bisexual reproduction - the so-called cyclic parthenogenesis. Thus, in some species of aphids, two-toed generations (winged forms) are replaced by parthenogenetic (wingless females), while different generations use different types of food plants.

Parthenogenetically, either an egg that has undergone meiosis and contains a haploid set of chromosomes (n) (generative, haploid, or meiotic parthenogenetic) can develop, or an egg from one of the premeiotic stages of oogenesis with preservation of the chromosome set characteristic of this species - diploid (2n) or polyploid (3n, 4n, 5n rarely 6n, 8n) (ameiotic parthenogenesis). In some forms of parthenogenesis, the fusion of the haploid nucleus of the egg with the haploid nucleus of the directional (polar) body leads to restoration of diploidity (automictic parthenogenesis). The genotype, sex of the parthenogenetic offspring, as well as the preservation or loss of heterozygosity, acquisition of homozygosity, etc., depend on these features of parthenogenesis.

Artificial parthenogenesis in animals was first obtained by a Russian zoologist A. A. Tikhomirov in 1886 by exposing unfertilized silkworm eggs to various physicochemical irritants (solutions of strong acids, friction, etc.) Subsequently, artificial parthenogenesis was obtained by J. Lebon and other scientists in many animals, for example, in marine invertebrates (sea urchins, stars, worms , mollusks), as well as in some amphibians (frogs), and even in mammals.

Artificial parthenogenesis is caused by the effect on the eggs of a hypertonic solution (hypotonic - osmotic parthenogenesis), the injection of an egg with a needle moistened with hemolymph (the so-called Traumatic parthenogenesis of amphibians), sudden heating or cooling (Temperature parthenogenesis), as well as the action of alkali acids, etc.

With the help of artificial parthenogenesis, it is usually possible to obtain only the initial stages of the development of an organism; complete parthenogenesis is rarely achieved.

Method of mass parthenogenesis developed for silkworms in 1936 by B. L. Astaurov. This method is based on precisely dosed short-term heating (up to 46 o C for 18 minutes) of unfertilized eggs removed from the female. The method makes it possible to obtain only female individuals, hereditarily identical with the maternal female (initial), as well as similar to each other, giving an increased yield of silk fiber of the highest quality.

Parthenogenesis also includes peculiar ways of development of animals and plants - gynogenesis and androgenesis, in which the eggs are activated for development by penetrating sperm of their own or a similar species, but the nuclei of the egg and sperm do not fuse. Fertilization turns out to be false, and the embryo develops with only a female (gynogenesis) or only a male (androgenesis) nucleus.

Thus, if American scientists’ experiment ends successfully, that is, healthy baby macaques are born, then experiments with human eggs will probably begin soon, especially since There are enough women volunteers.

Infertile and lesbian couples are most interested in this. However, they must take into account that only girls can be born. For now, scientists do not intend to conduct similar experiments on humans, since there is a serious risk of developing cancer and metabolic disorders in newborns, and also because we have genes that only work if they are received from the father. It is in them that the proteins necessary for the development of tissues and organs are encoded. Therefore, it is unlikely that women will be able to do without men, at least in the near future, while man is not able to outwit nature.

Daughter organisms develop from unfertilized eggs. Opened in the middle of the 18th century. Swiss naturalist III. Bonnet.

The meaning of parthenogenesis:

1) reproduction is possible with rare contacts of opposite-sex individuals;

2) the population size increases sharply, since the offspring are usually numerous;

3) occurs in populations with high mortality within one season.

Types of parthenogenesis:

1) obligate (obligatory) parthenogenesis. It is found in populations consisting exclusively of female individuals (in the Caucasian rock lizard). At the same time, the probability of meeting different-sex individuals is minimal (the rocks are separated by deep gorges). Without parthenogenesis, the entire population would be on the verge of extinction;

2) cyclic (seasonal) parthenogenesis (in aphids, daphnia, rotifers). Occurs in populations that have historically died out in large numbers at certain times of the year. In these species, parthenogenesis is combined with sexual reproduction. Moreover, in the summer there are only females who lay two types of eggs - large and small. From large eggs, females emerge parthenogenetically, and from small eggs, males emerge, which fertilize the eggs lying on the bottom in winter. Only females emerge from them;

3) facultative (optional) parthenogenesis. Found in social insects (wasps, bees, ants). In a population of bees, fertilized eggs produce females (worker bees and queens), while unfertilized eggs produce males (drones).

In these species, parthenogenesis exists to regulate

numerical sex ratio in the population.

There are also natural (exists in natural populations) and artificial (used by humans) parthenogenesis. This type of parthenogenesis was studied by V.N. Tikhomirov. He achieved the development of unfertilized silkworm eggs by irritating them with a thin brush or immersing them in sulfuric acid for a few seconds (only females are known to produce silk thread).

Gynogenesis(in bony fish and some amphibians). The sperm penetrates the egg and only stimulates its development. In this case, the sperm nucleus does not stick together with the egg nucleus and dies, and the source of hereditary material for the development of the offspring is the DNA of the egg nucleus.

Androgenesis. The development of the embryo involves the male nucleus introduced into the egg, and the nucleus of the egg dies. The egg cell provides only nutrients from its cytoplasm.

Polyembryony. The zygote (embryo) is divided into several parts asexually, each of which develops into an independent organism. Found in insects (riders), armadillos. In armadillos, the cellular material of initially one embryo at the blastula stage is evenly divided between 4-8 embryos, each of which subsequently gives rise to a full-fledged individual.