Recently, scientists at the Institute for the Development of Cell Technology (Massachusetts, USA) obtained full-fledged embryos from unfertilized eggs from 4 of 28 monkeys tested. They were able to achieve such results thanks to a chemical drug under the influence of which a special way of reproduction occurs - "parthenogenesis". What is parthenogenesis?
Parthenogenesis(Parthenogenesis - from the Greek parthenos - girl, virgin + genesis-origin) - a form of sexual reproduction, in which the development of the body occurs from the female reproductive cell (egg) without fertilization of her male (sperm).
Parthenogenesis should be distinguished from asexual reproduction, when development does not occur from germ cells, but from somatic cells or organs by division, budding.
It's sexual, but same-sex reproduction, which arose in the process of 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 able to leave offspring. If a female develops from fertilized eggs, and a male develops from unfertilized eggs, parthenogenesis contributes to the regulation of the number and sex ratio(for example, bees develop parthenogenetically males - drones, and from fertilized bees - females - queens and worker bees).
Parthenogenesis - natural the normal way of reproduction of some species of animals and plants... Complete natural parthenogenesis occurs in invertebrates of all types, but most often in arthropods. Of the vertebrates, these are fish of some species of amphibians, reptiles, individual species of birds (turkeys) reproduce parthenogenetically. In mammals, only cases of embryonic parthenogenesis are known, isolated cases of full development were observed in a rabbit with artificial parthenogenesis. In man 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 are known in history. Africa and European countries).
Parthenogenesis can be obligate when 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 - the so-called cyclic parthenogenesis. So 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 cell that has undergone meiosis and contains a haploid set of chromosomes (n) (generative, haploid, or meiotic parthenogenetic) can develop, or an egg cell of one of the premeiotic stages of oogenesis while maintaining the chromosome set characteristic of this type - diploid (3n) or polyploid 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 the restoration of diploidy (automictic parthenogenesis). The genotype, sex of the partogenetic offspring, as well as the preservation or loss of heterozygosity, the 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 stimuli (solutions of strong acids, friction, etc.). , molluscs), as well as in some amphibians (frogs), and even in mammals.
Artificial parthenogenesis is caused by action on eggs with a hypertonic solution (hypotonic - osmotic parthenogenesis), pricking the egg with a needle moistened with hemolymph (the so-called Traumatic parthenogenesis of amphibians), sharp 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.
Mass parthenogenesis method developed for the silkworm in 1936 by B. L. Astaurov... This method is based on precisely dosed short-term heating (up to 46 o C for 18 minutes) unfertilized eggs extracted from the female. The method allows to obtain individuals of only female sex, hereditarily identical with the maternal female (original), as well as similar to each other, giving an increased yield of silk fiber of the highest quality.
Parthenogenesis also includes the 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 closely related species, but the nuclei of the egg and sperm do not fuse. Fertilization turns out to be false, and the embryo develops only with a female (gynogenesis) or only with a male (androgenesis) nucleus.
Thus, if the experiment of American scientists ends successfully, that is, healthy young macaques are born, then experiments with human eggs will probably begin soon, especially since there are enough women volunteers.
The most interested in this are infertile and lesbian couples. However, they should take into account that only girls can be born. In the meantime, scientists do not intend to conduct such experiments on humans, since there is a serious risk of developing cancer and metabolic disorders in newborns, as well as the fact that we have genes that only work if they are obtained 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, in any case, in the near future, until a person is able to outwit nature.
Surely each of you knows the story described in Scripture. Mary, being the chosen one of God, gave birth to an immaculately conceived child. Whether this actually happened or was only the result of the violent imagination of the authors of those times, today it is difficult to say. But let it be known to you, the virgin birth in our world is quite common. What is parthenogenesis and what is its essence?
Amazing world
Perhaps, the origin of life can be attributed to one of the greatest mysteries of our universe. Where did it come from and who is the creator of everything and everyone is a mystery sealed with seven seals. But whoever our creator was, he took great care to ensure that life on the blue planet never runs out. Its various forms inhabiting the Earth are able to reproduce their own kind in the most diverse, sometimes very unexpected ways.
Parthenogenesis
What is parthenogenesis? This is the ability of the female to give life 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 the female for some reason could not find a mating partner and fertilization of the egg did not happen, she will still be able to produce full-fledged offspring without his participation. This ability provides the species with very good survival rates. When the number decreases, females can replenish the population and continue the race for a short time. 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 from unfertilized eggs, drones (males) appear, and from fertilized eggs - working individuals, which are all female.
Types of parthenogenesis
What is parthenogenesis and how can it proceed in certain animals? In some species, it is considered the main breeding method (obligate). For other forms, it is cyclical, that is, periodically offspring appears from unfertilized eggs, but more often with the participation of a male. The optional, 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, the exception, because usually such animals adhere to bisexual reproduction.
Parthenogenesis in animals
What is parthenogenesis? This is the process by which the parental 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 of 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 gave impetus to the emergence of some directions in the industry. So, scientists learned that parthenogenesis in the silkworm starts after exposure to certain temperatures. This greatly accelerated the breeding process for these insects.
The essence of parthenogenesis is well known to beekeepers and silk producers; many invertebrates use this method. some types of lizards, fish are often practiced, 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 initiate parthenogenesis in warm-blooded animals. Unfortunately, it is impossible to give examples, since in some people the growth of cells and the development of embryos took place, but things never came to the final stage. From the side of medicine, considerable interest is also aroused. A survey was conducted, after which it became known that most married couples who cannot have a baby would gladly decide on such an immaculate conception. Who knows, maybe over time the veil of secrecy will be lifted. And the miracle will come true - parthenogenesis will be able to give life to a human baby.
Many animals develop eggs without. This form of sexual breeding are called parthenogenesis... Reproduction by parthenogenesis was first described in aphids. Currently, a distinction is made between natural and artificial parthenogenesis.
Natural parthenogenesis
Natural parthenogenesis it is periodic and optional. With periodic parthenogenesis, it alternates with normal sexual reproduction (aphids). Facultative parthenogenesis is characteristic of bees, ants, etc. In them, the uterus lays fertilized and unfertilized eggs. In bees, queen and worker bees develop from fertilized eggs, and males (drones) from unfertilized eggs.Artificial parthenogenesis
Artificial parthenogenesis caused in animals that normally reproduce with. For the first time, artificial parthenogenesis was obtained by A.A. Tikhomirov at the silkworm. Subsequently, B.L. Astaurov. Artificial parthenogenesis can be caused by a combination of various factors: rubbing eggs with a brush, exposure to weak sulfuric acid, blood serum, fat solvents, electrical influences, etc.With sexual reproduction, offspring is obtained as a result of the fusion of the genetic material of the haploid nuclei. Usually these nuclei are contained in specialized germ cells - gametes; during fertilization, the gametes merge, forming a diploid zygote, from which a mature organism is obtained in the process of development. Gametes are haploid - they contain one set of chromosomes resulting from meiosis; they serve as a link between this generation and the next (during sexual reproduction of flowering plants, not cells, but nuclei merge, but usually these nuclei are also called gametes).
Meiosis is an important stage in the life cycle involving sexual reproduction, as it leads to a decrease in the amount of genetic material in half. Due to this, in a series of sexually reproducing generations, this amount remains constant, although with fertilization it doubles each time. During meiosis, as a result of random divergence of chromosomes (independent distribution) and the exchange of genetic material between homologous chromosomes (crossing over), new combinations of genes appear in the same gamete, and this shuffling increases genetic diversity. The fusion of the haploid nuclei contained in the gametes is called fertilization or syngamia; it leads to the formation of a diploid zygote, that is, a cell containing one chromosome set from each parent. This union of two sets of chromosomes in the zygote (genetic recombination) is the genetic basis for intraspecific variation. The zygote grows and develops into a mature organism of the next generation. Thus, during sexual reproduction in the life cycle, the diploid and haploid phases alternate, and in different organisms these phases take on different forms.
Gametes are usually of two types, male and female, but some primitive organisms produce only one type of gametes. In organisms that form gametes of two types, they can be produced by male and female parent individuals, respectively, or it may be so that the same individual has both male and female genital organs. Species that have separate males and females are called dioecious; most animals and humans are like that. Among flowering plants, there are also dioecious species; if in monoecious species male and female flowers are formed on the same plant, as, for example, in cucumber and hazel, then in dioecious species some plants bear only male, and others only female flowers, like in holly or yew.
Parthenogenesis
Parthenogenesis is one of the modifications of sexual reproduction, in which the female gamete develops into a new individual without fertilization by the male gamete. Parthenogenetic reproduction occurs in both the animal and plant kingdoms and has the advantage that in some cases it increases the rate of reproduction.
Distinguish between natural parthenogenesis - the normal way of reproduction of some organisms in nature and artificial, caused experimentally by the action of various stimuli on an unfertilized egg, which normally needs fertilization. Classification of parthenogenesis:
Obligate - when it is the only way to reproduce
Cyclic - parthenogenesis naturally alternates with other methods of reproduction in the life cycle (for example, in daphnia and rotifers).
Optional - occurring as an exception or a reserve mode of reproduction in forms that are normally bisexual.
There are two types of parthenogenesis - haploid and diploid, depending on the number of chromosomes in the female gamete. In many insects, including ants, bees, and wasps, as a result of haploid parthenogenesis, various castes of organisms arise within a given community. In these species, meiosis occurs and haploid gametes are formed. Some eggs fertilize and develop into diploid females, while unfertilized eggs develop into fertile haploid males. For example, in a honey bee, the queen lays fertilized eggs (2n = 32), which, while developing, give females (queens or workers), and unfertilized eggs (n = 16), which give males (drones), which produce sperm through mitosis, and no meiosis. Such a reproduction mechanism in social insects has an adaptive value, since it allows one to regulate the number of offspring of each type. In aphids, diploid parthenogenesis occurs, in which female oocytes undergo a special form of meiosis without chromosome divergence - all chromosomes pass into the egg, and polar bodies do not receive a single chromosome. Eggs develop in the mother's body, so that young females are born fully formed rather than hatching from eggs. This process is called live birth. It can continue for several generations, especially in summer, until almost complete divergence occurs in one of the cells, resulting in a cell containing all pairs of autosomes and one X chromosome. The male develops parthenogenetically from this cell. These autumn males and parthenogenetic females produce haploid gametes as a result of meiosis, which participate in sexual reproduction. Fertilized females lay diploid eggs, which overwinter, and in the spring they hatch into females that reproduce parthenogenetically and give birth to living offspring. Several parthenogenetic generations are replaced by a generation resulting from normal sexual reproduction, which introduces genetic diversity into the population as a result of recombination. The main advantage that parthenogenesis gives to aphids is the rapid growth of the population, since at the same time all its sexually mature members are capable of laying eggs. This is especially important during periods when environmental conditions are favorable for the existence of a large population, i.e. in the summer months.
Parthenogenesis is widespread in plants, where it takes various forms. One of them - apomixis - is parthenogenesis, which mimics sexual reproduction. Apomixis is observed in some flowering plants in which a diploid ovule cell, or a nucellus cell, or a megaspore develops into a functional embryo without the participation of the male gamete. From the rest of the ovule, a seed is formed, and from the ovary, a fruit develops. In other cases, the presence of a pollen grain is required, which stimulates parthenogenesis, although it does not germinate; a pollen grain induces hormonal changes necessary for the development of the embryo, and in practice such cases are difficult to distinguish from real sexual reproduction.
Fertilization occurs in a peculiar way in flowering plants. After fertilization, a seed is formed from the ovule, containing the embryo and a supply of nutrients. How is the supply of nutrients formed in the seed?
In flowering plants, double fertilization occurs. When pollinated, a pollen grain falls on the stigma of the pistil and germinates, forming a pollen tube. It is formed from a vegetative cell and grows rapidly, reaching the ovary. At the end of the pollen tube are two sperm.
Unlike motile spermatozoa of lower plants, sperm in flowering plants are immobile and can penetrate to the egg cell only through the pollen tube.
The pollen tube grows into the ovule, its tip breaks, and the sperm enter the embryo sac. One of them fuses with the egg. A diploid cell is formed - a zygote. The second sperm is fused with the diploid secondary nucleus of the embryo sac. As a result, a cell with a triple set of chromosomes is formed, from which endosperm is formed by repeated mitoses - a tissue containing a supply of nutrients.
Hermaphroditism
Conjugation
Conjugation (Latin "conjugatio" - connection) is a form of sexual process without the participation of gametes. It is characteristic of Escherichia coli (bacteria department), ciliates-shoes (Protozoa type), in which two unicellular individuals approach each other and exchange genetic material through the cytoplasmic bridge.
Fig. 4
As a result of conjugation, bacteria do not increase the number of individuals. In the green alga Spirogyra, conjugation occurs in a different way: two multicellular filaments stand parallel to each other, form opposite cytoplasmic bridges, along which the protoplast of a physiologically male individual flows into the female thread. As a result, many zygotes are formed.
Copulation
In some unicellular organisms, a type of sexual process is observed, which is called copulation. Copulation (from Lat. "Copulatio" - connection) - the process of fusion of two sex cells.
During copulation (in protozoa), the formation of genital elements and their pairwise fusion occur. In this case, two individuals acquire sex differences and completely merge, forming a zygote. The unification and recombination of the hereditary material occurs, therefore the individuals are genetically different from the parental ones.
Parthenogenesis(from the Greek παρθενος - virgin and γενεσις - birth, in plants - apomixis) - the so-called "virgin reproduction", one of the forms of sexual reproduction of organisms, in which female reproductive cells (eggs) develop into an adult organism without fertilization. Although parthenogenetic reproduction does not involve the fusion of male and female gametes, parthenogenesis is still considered sexual reproduction, since the organism develops from the germ cell. It is believed that parthenogenesis arose during the evolution of organisms in dioecious forms.
In cases where parthenogenetic species are represented (always or periodically) only by females, one of the main biological advantages parthenogenesis is to accelerate the rate of reproduction of the species, since all individuals of such species are able to leave offspring. This method of reproduction is used by some animals (although more often relatively primitive organisms resort to it). In cases where females develop from fertilized eggs, and males develop from unfertilized eggs, parthenogenesis contributes to the regulation of the numerical ratios of sexes (for example, in bees). Often parthenogenetic species and races are polyploid and arise as a result of distant hybridization, thereby revealing heterosis and high viability. Parthenogenesis should be attributed to sexual reproduction and should be distinguished from asexual reproduction, which is always carried out with the help of somatic organs and cells (reproduction by division, budding, etc.).
Classifications of parthenogenesis
There are several classifications of parthenogenetic reproduction.
By breeding method
Natural - The normal way some organisms reproduce in nature.
Artificial - is caused experimentally by the action of various stimuli on an unfertilized egg, which normally needs fertilization.
By the completeness of the flow
Rudimentary (rudimentary) - unfertilized eggs begin to divide, but embryonic development stops in the early stages. At the same time, in some cases, it is possible to continue development to the final stages (accidental or accidental parthenogenesis).
Full - the development of the egg leads to the formation of an adult. This type of parthenogenesis is observed in all types of invertebrates and in some vertebrates.
By the presence of meiosis in the development cycle
Ameiotic - developing eggs do not undergo meiosis and remain diploid. Such parthenogenesis (for example, in daphnia) is a type of clonal reproduction.
Meiotic - the eggs undergo meiosis (thus they become haploid). A new organism develops from a haploid ovum (male hymenopterans and rotifers), or the ovum in one way or another restores diploidy (for example, by endomitosis or fusion with a polar body)
By the presence of other forms of reproduction in the development cycle
Obligate - when it is the only way to reproduce
Cyclic - parthenogenesis naturally alternates with other methods of reproduction in the life cycle (for example, in daphnia and rotifers).
Optional - occurring as an exception or a reserve mode of reproduction in forms that are normally bisexual.
Depending on the sex of the body
Gynogenesis - female parthenogenesis
Androgenesis - male parthenogenesis
Prevalence
In animals
] In arthropods
The ability for parthenogenesis in arthropods has tardigrades, aphids, balanus, some ants, and many others.
In ants, telytoxic parthenogenesis was found in 8 species and can be divided into 3 main types: type A - females produce females and workers through telitokia, but workers are sterile and males are absent ( Mycocepurus smithii); type B - workers produce workers and potential females through telitokia; type C - females produce females by telytokia, and workers - by normal sexual means, while workers produce females through telytokia. Males are known for types B and C. Type B is found in Cerapachys biroi, two myrmycin species, Messor capitatus and Pristomyrmex punctatus, and in the ponerine species Platythyrea punctata... Type C found in runner ants Cataglyphis cursor and two myrmycin species Wasmannia auropunctata and Vollenhovia emeryi .
In vertebrates
Parthenogenesis is rare in vertebrates and occurs in about 70 species, accounting for 0.1% of all vertebrates. For example, there are several species of lizards that reproduce in natural conditions by parthenogenesis (Darevskia, Komodo monitor lizards). Parthenogenetic populations have also been found in some species of fish, amphibians, and birds (including chickens). Cases of same-sex reproduction are not yet known only among mammals.
Parthenogenesis in Komodo monitor lizards is possible because ovogenesis is accompanied by the development of a polocyte (polar body) containing a double copy of the egg's DNA; In this case, the polocyte does not die and acts as a sperm, turning the egg into an embryo.
In plants
A similar process in plants is called apomixis. It can be vegetative propagation, or propagation by seeds that have arisen without fertilization: either as a result of a type of meiosis that does not halve the number of chromosomes, or from diploid ovule cells. Since many plants have a special mechanism: double fertilization, then in some of them (for example, in several types of Potentilla), pseudogamy is possible - when seeds are obtained with an embryo that develops from an unfertilized egg, but contain triploid endosperm resulting from pollination and subsequent triple fusion: 83.
Induced "parthenogenesis" of mammals
At the beginning of 2000. it was shown that by in vitro treatment of mammalian oocytes (rats, macaques, and then humans) or by preventing the separation of the second polar body during meiosis, it is possible to induce parthenogenesis, while development in culture can be brought to the blastocyst stage. Thus obtained human blastocysts are potentially a source of pluripotent stem cells that can be used in cell therapy.
In 2004, in Japan, by the fusion of two haploid oocytes taken from different mice, it was possible to create a viable diploid cell, the division of which led to the formation of a viable embryo, which, having passed the blastocyst stage, developed into a viable adult. It is assumed that this experiment confirms the participation of the role of genomic imprinting in the death of embryos formed from oocytes obtained from one individual at the blastocystal stage.
The significance of parthenogenesis lies in the possibility of reproduction during rare contacts of heterosexual individuals (for example, on the ecological periphery of the range), as well as in the possibility of a sharp increase in the number of offspring (which is important for species and populations with high cyclic mortality).
The phenomenon of parthenogenesis was first established by the English scientist Ovel in 1849.
Partenogenes (from the Greek "partenos" - virgin and "qenesis" - origin), virgin development, one of the forms of sexual reproduction of organisms, in which female reproductive cells develop without fertilization. Biologically, this type of reproduction is less complete than development after fertilization. since there is no fusion of maternal and paternal heredity. The significance of parthenogenesis lies in the possibility of reproduction with rare contacts of heterosexual individuals (at the periphery of the range), as well as in the possibility of a sharp increase in the number of offspring.
Parthenogenesis occurs in some lower crustaceans, insects (aphids, bees, wasps, ants), lizards, sometimes in birds (turkeys) and most often alternates with typical sexual reproduction.
Parthenogenesis is especially widespread among daphnia. Cyclic parthenogenesis is observed in these individuals. During spring and summer, animals reproduce only parthenogenetically. Only females develop from unfertilized eggs. At the end of summer, females lay small and large eggs. Males develop from small eggs, females develop from large eggs.
The last female populations lay fertilized eggs, which overwinter. In the spring of them, females develop again, which reproduce parthenogenetically until autumn.
In aphids, in spring, wingless females - “founders” emerge from wintering fertilized eggs, which give several generations of wingless parthenogenetic females. At the end of summer, winged females "fruit-bearing" develop from parthenogenetic eggs. They give, like daphnia, small and large eggs, from which males and females develop respectively. Females lay fertilized eggs, which overwinter and the next year give birth to “founders” again. The main advantage that parthenogenesis gives to aphids is the rapid growth of the population, since all its sexually mature members are capable of laying eggs. This is especially important during the period when environmental conditions are favorable for the existence of a large population, that is, during the summer months.
Parthenogenetic development also occurs in social insects such as ants and bees. As a result of parthenogenesis, various castes of organisms arise. Such reproduction has an adaptive value, since it allows you to regulate the number of offspring of each type.
(The student briefly explains a diagram illustrating the role of parthenogenesis in the life cycle of a honey bee colony)
(fertile female)
(Larva gets Uterus Mitosis 
royal jelly)
Fertilized
egg (2n = 32) (The larva receives
honey and pollen)
(The larva receives an unfertilized drone
honey and pollen) egg (n = 16) Parthenogenesis (n = 16)
Working specimen
(sterile female)
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