Parthenogenesis (from the Greek ldquo;parthenosrdquo; - ldquo;virginrdquo; and ldquo;genesisrdquo;) or, as it is called, a virgin reproduction

Parthenogenesis [Virgin reproduction, without fertilization, Types]

Parthenogenesis (from the Greek “parthenos” — “virgin” and “genesis”) or, as it is called, a virgin reproduction is a special way of sexual reproduction. In parthenogenesis the embryo development begins with unfertilized egg, i.e. merging of egg and sperm nuclei doesn’t occur. This is a paradoxical case of sexual reproduction, when reproduction of their own kind by a gamete is carried out without the fertilization. At present there are known thousands of species of plants and animals which reproduce by parthenogenesis (diagram 16). This reproduction method is described in many species of plants, flatworms and oligochaetes, crustaceans, arachnids and insects. Among vertebrates in its natural form it is found in fish, amphibians and reptiles. Birds and mammals — one of the few animals in which parthenogenesis in nature does not happen.

In the laboratory, in some types of poultry parthenogenetic reproduction can be done, but as result born not females like in a goldfish and lizards, but males. And this is natural, since in birds male is homogametic.

There are several types of parthenogenesis.

Diagram 16. Some parthenogenetic species of fauna: a — aphids; b - daphnia; c — earthworm dendrobaena octaedra; d — the Prussian carp

Automictic (haploid) parthenogenesis

Parthenogenetic reproduction of hymenoptera (parasitoid wasps, ants, bees, wasps, etc.) is a true parthenogenesis. With this method of reproduction from an unfertilized egg develops male whose body consists of haploid cells, and from the fertilized — diploid female. This type is also called haploid parthenogenesis.

Facultative (cyclical) parthenogenesis

Cyclical (facultative) parthenogenesis (or heterogamy, heterogony) occurs in aphids and daphnia. During the favorable for the life summer months from the unfertilized diploid eggs appear females, which, in turn, give rise to new generations of parthenogenetic females. So during the season it occurs several times. When autumn comes, from immature eggs (due to the cold water) appear males participating in reproduction. During this period, in females occurs meiosis, and they produce haploid eggs that overwinter in a fertilized form. In spring from overwintered diploid eggs appear again parthenogenetic females. Thus the cycle closes.

Apomictic (clonal) parthenogenesis

Apomictic (clonal) parthenogenesis is a method of reproduction that is inherent in many types of plants, planarians, earthworms, carps, rock lizards and oceanic geckos. In this case, the development of the embryo begins in unfertilized oocytes and never accompanied by changes of bisexual and unisexual generations, like in aphids or daphnia. The eggs can contain two, three, four, and in earthworms — five, eight or even ten chromosome sets. Thus descendants (all are females) are exact genetic copies of the mother. Therefore, they are, as in the vegetative reproduction, called the clones. This method of sexual reproduction, in which forms the female clone, is called apomixis (from Greek “apo” — “without” and “mixis”) in the scientific literature. Taken from http://worldofschool.org

Obligate (sperm-dependent) parthenogenesis (gynogenesis)

An interesting type of parthenogenesis is a clonal gynogenesis (from Greek “gines” — “woman” and “genesis”), or as it is called, sperm-dependent (or obligate) parthenogenesis. This method of sexual reproduction is common in freshwater fish, including Prussian carp (diagram 16, d). In this case, the offspring, which is composed entirely of clonal females, also comes from unfertilized eggs. However, the cleavage of eggs in gynogenetic females is necessarily initiated by the sperm of other species of fish. The fusion of the nuclei, and hence, fertilization do not occur. Therefore, this type of interaction between sperm and egg is also called pseudogamy or pseudo fertilization.

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Questions:
  • Why parthenogenesis is also called a virgin reproduction?

  • What groups of animals have haploid parthenogenesis, and what — diploid?

  • Why mammals cannot reproduce by parthenogenesis?