Study Confirms Virgin Birth

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Study Confirms Virgin Birth

Scientists have solved the mystery of how a baby shark appeared in a tank of females without the help of a male: it was a virgin birth. The bonnethead shark was born through "parthenogenesis", a process where an egg develops into an embryo without being fertilised by sperm.

Virgin births, possible in some birds, amphibians, reptiles and bony fishes, are extremely rare. It had never before been confirmed in cartilaginous fish, such as sharks and rays. The birth, in 2001, astonished scientists as placental animals, including this shark, were thought to need genetic material from sperm and egg to produce viable young.

The genetic tests on the shark - finally published after six years - confirmed this was a virgin birth.

From : Guardian

Parthenogenesis is a form of asexual reproduction in which females produce eggs that develop without fertilization. Parthenogenesis is seen in aphids, daphnia, rotifers, and some other invertebrates, as well as in some plants. Most recently Komodo Dragons and sharks have been added to this list. Among vertebrates, there are several genera of fish, amphibians, and reptiles that exhibit differing forms of asexual reproduction, including true parthenogenesis, gynogenesis, and hybridogenesis (an incomplete form of parthenogenesis).

The offspring of parthenogenesis will be all female if two like chromosomes determine the female sex (such as systems where XX is female and XY is male), but male if the female sex is determined by unlike chromosomes (such as systems where WZ is female and ZZ is male), because the process involves the inheritance and subsequent duplication of only a single sex chromosome. The offspring may be capable of sexual reproduction, if this mode exists in the species. A parthenogenetic offspring is sometimes called a parthenogen. As with all types of asexual reproduction, there are both costs (reduced genetic diversity generated and susceptibility to adverse mutation) and benefits (reproduction without the need for a mate) associated with parthenogenesis.

Parthenogenesis is distinct from artificial animal cloning, a process where the new organism is identical to the cell donor. Parthenogenesis is truly a reproductive process which creates a new individual or individuals from the naturally varied genetic material contained in the eggs of the mother. A litter of animals resulting from parthenogenesis may contain all genetically unique siblings without any twins or multiple numbers from the same genetic material. Parthenogenic offspring of a parthenogen are, however, all genetically identical to each other and to the mother, as a parthenogen is homozygous.

The alternation between parthenogenesis and sexual reproduction is called heterogamy. Forms of reproduction related to parthenogenesis but that require the presence of sperm are known as gynogenesis and hybridogenesis.
By IAF: posted on 24-5-2007

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