CBSE Class 12 Biology Parthenogenesis Notes

 PARTHENOGENESIS

(VIRGIN REPRODUCTION OR VIRGIN BIRTH)

Parthenogenesis is the development of an egg into offspring without fertilization.

Occurance: It is very common in Rotifers, Aphids, Bees and crustacean. Some vertebrates also reproduced by parthenogenesis.

Types: Parthenogenesis may be natural or artificial.

1 ) Natural parthenogenesis: It occurs regularly in the life cycle of some animals and is of following two types:

a) Complete parthenogenesis: It is also called as obligatory parthenogenesis . It means individuals with complete parthenogenesis,the males are completely absent and the females develop from the unfertilized eggs as it is found in Aphids, Phyllopods and Rotifers. It is also founds in some vetebrates. For example, a lizard Lacerta sexicola americana reproduce exclusively by parthenogenesis with no males in the population.

b) Incomplete parthenogenesis : In cyclic parthenogenesis, sexual generation alternates with parthenogenesic generation. For example, in bees and wasps, some eggs develop without fertilization and produce males, while those eggs that are fertilized developed into females. 

PAEDOGENETIC PARTHENOGENESIS: In Gall Fly, the larvae may lay eggs which develop parthenogenetically into a new generation of larvae. This is called paedogenesis.

2) Artifical Parthenogenesis: In many sexually reproducing animals the egg can be activated by artificial methods to start the development without fertilization. This is called artificial parthenogenesis. For example, eggs of Sea Urchin can be made to develop successfully, if treated with weak salt solutions (chlorides of sodium ,potassium calcium and magnesium),weak organic acids, electric shocks or by shaking in sea water or by pricking the egg with glass needle.

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