Parthenogenesis call a form of sexual reproduction at which the organism develops from not impregnated female gamete. It meets at all invertebrates and vertebrate animals, except for mammals. Allocate two of its main forms — ginogenez and an androgenesis.
The parthenogenesis is called still virgin reproduction, this process is characteristic of types at which short vital the cycle is followed by the expressed seasonal changes.
Androgenesis and ginogenez
In the course of an adrogenez the female gamete does not take part in development of a new organism which appears as a result of merge of two kernels of men's gametes — spermatozoa. In this case at posterity there are only males. In the nature the androgenesis meets at hymenopterous insects.
At a ginogeneza the kernel of a spermatozoon does not merge with an ovum kernel, it can only stimulate its development, there is a so-called false fertilization. This process is peculiar to Amphibia, bony fishes and roundworms, at the same time the posterity consists only of females.
Haploid and diploidic parthenogenesis
At a haploid parthenogenesis the organism develops from a haploid ovum, at the same time individuals can be female, men's or both that and others, everything depends on chromosomal sex determination at this look. At ants, bees and wasps as a result of a parthenogenesis the males appear from not oosperms, and a female from impregnated. Thanks to it organisms are divided into castes, process allows to regulate the number of descendants of a certain type. At some lizards, plant louses and the kolovratok is observed a diploidic parthenogenesis, it is called still somatic. At the same time at females diploidic ova are formed. The number of individuals allows to support this process if the meeting of individuals of a different floor is complicated.
Natural and artificial parthenogenesis
The parthenogenesis has cyclic character at a kolovratok, plant louses and water fleas. In summertime there are only females, they develop parthenogenetic, and in the fall reproduction takes place with fertilization. This process is characteristic of the animals perishing in a large number, for example, at helminths it provides intensive reproduction, despite their mass death during life cycle. The natural parthenogenesis, so-called apomixis also meets at a number of plants, at the same time the germ appears not from gametes or from not impregnated ovum. The parthenogenesis can be caused artificially, for example, by irritation of a surface of eggs of a silkworm, heating or influence of various acids, it is possible to achieve crushing of egg without fertilization. Parthenogenetic it was succeeded to receive adult rabbits and frogs.