Parthenogenesis

Parthenogens, unlike sexually reproducing animals, are faced with the unique problem of how to maintain a complete set of chromosomes. Chromosomes are cellular structures composed of DNA and protein that contain the genetic information cells need to function properly. In animals that reproduce sexually, reduction division (meiosis) occurs in cells destined to become eggs or sperm. Meiosis is the process where the chromosome content of a dividing cell is divided and reduced, producing egg or sperm cells with only half the normal number of chromosomes. When an egg is fertilized the chromosomes from the sperm are injected into the egg so restoring the fertilized egg's chromosome number to that of the parents' body cells. Fertilization does not occur in parthenogenetic animals, which have developed special mechanisms to insure that a full set of chromosomes are passed on to the next generation.

The cellular mechanisms by which parthenogenetic animals maintain a full set of chromosomes are known as apomixis and automixis. Each mechanism either alters or suppresses meiosis. Apomictic parthenogens are those in which meiosis is completely suppressed whereas automictic parthenogens are those in which the early stages of meiosis occur but the event is altered so that no chromosome division results.