Parthenogenesis

Recently, the New England Aquarium in the US announced that a “virgin” anaconda had given birth during the winter. The aquarium does not have a male anaconda. Yet Anna, a green female anaconda, gave birth to a few babies, two of which have survived. In scientific terminology, it is known as parthenogenesis.

Parthenogenesis:

• The term parthenogenesis is an amalgam of the Greek words parthenos meaning virgin and genesis meaning origin.
• It is an asexual reproductive strategy that involves development of a female (rarely a male) gamete (a mature germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote) without its fertilisation.
• It occurs commonly among lower plants and invertebrate animals (particularly rotifers, aphids, ants, wasps and bees) and rarely among higher vertebrates.
• Many species that reproduce through parthenogenesis do not reproduce sexually. Others switch between the two modes taking cues from the environment.

Characteristics of Parthenogenesis:

• Babies born through parthenogenesis are clones of the mother. This was proved by this New England Aquarium through DNA tests.
• Parthenogenetic offspring tend to be clones of the parent because there has been no exchange and rearrangement of genetic information with another individual as happens in case of a sexual reproductive process.
• Stillbirth is common in parthenogenesis.

Mechanism of Parthenogenesis:

• Offspring of parthenogenic species develop from gametes. Gametes are reproductive cells that result from meiosis—in which a specialized cell with a (diploid) double set of chromosomes undergoes two fissions of its nucleus. Meiosis gives rise to four gametes, or sex cells, which are haploid—in that each possesses half the number of chromosomes of the original cell.
• Parthenogenesis can operate on either a haploid or a diploid cell. In haploid parthenogenesis, a rare form of parthenogenesis that occurs in a few species of bees, nematodes, and plants, offspring develop from haploid eggs to produce haploid adults.
• On the other hand, the process of diploid parthenogenesis, a more common and varied form of the phenomenon, may proceed along two pathways.
• Automixis (automictic parthenogenesis) is a postmeiotic process in which a haploid cell may either duplicate its chromosomes or join with another haploid cell. In both cases, diploid zygotes develop and grow into diploid adults. Such organisms are not true clones of the mother, however, because the meiotic process separates and recombines the genetic material.
• A second form of diploid parthenogenesis, apomixis (apomicitic parthenogenesis), forgoes complete meiosis altogether. Instead, two genetically identical diploid egg cells are produced from a parent cell through mitosis (the process of cell duplication), and one or more of these daughter cells, which are both diploid and clones (that is, genetically identical) of the original parent cell, develop into a diploid offspring.
• Diploid parthenogenesis occurs in insects such as aphids as well as in some rotifers and flowering plants.