PARTHENOGENESISparthenos "virgin" and genesis "creation"

Reproduction without fertilization

Parthenogenesis• More specifically, it occurs when a female gamete

develops a new individual without being fertilized by a male gamete.

• It is NOT a form of "asexual reproduction," but an incomplete form of sexual reproduction.

• This is because it involves the production, activation, and development of a female egg which is a specialized reproductive cell.

ParthenogenesisIn what organisms does parthenogenesis occur?• Occurs in many types of plants

• Invertebrates honeybees, aphids, ants, some scorpions and many others

• Few vertebrates komodo dragons, mole salamenders, hammerhead sharks, some reptiles, some amphibians, some fish, rarely in birds

• Can be artificially induced (even in mammals)

Parthenogenesis in HoneybeesHoney bees are also able to reproduce without fertilization, although the purpose of the parthenogenesis reproduction is slightly different than in other animals.

The queen bee only mates once during her lifetime (although she may mate with many male bees during that time).

The sperm is used to fertilize some of her eggs, which will become female worker bees. Her unfertilized eggs will grow into bees via parthenogenesis and will all be male drones.

http://www.youtube.com/watch?v=VsCmSWoF8PY

Parthenogenesis in Komodo Dragons

A baby Komodo dragon hatches from an unfertilized egg at the London Zoo.

http://www.youtube.com/watch?v=G41EANkcMvg

• Most reptiles reproduce sexually, but parthenogenesis has been observed in certain species of rock lizards, geckos, whiptails, and Komodo Dragons.

• Recently, the Komodo dragon which normally reproduces sexually was found to also be able to reproduce by parthenogenesis. Because the genetics of sex determination in Komodo Dragons uses the WZ system (where WZ is female, ZZ is male, WW is inviable) the offspring of this process will be ZZ (male) or WW (inviable), with no WZ females being born.

• A case has been documented of a Komodo Dragon switching back to sexual reproduction after a parthenogenetic event. It has been postulated that this gives an advantage to colonisation of islands, where a single female could theoretically have male offspring asexually, then switch to sexual reproduction to maintain higher level of genetic diversity than asexual reproduction alone can generate.

• Parthenogenesis may also occur when males and females are both present, as the wild Komodo dragon population is approximately 75 per cent male.

Parthenogenesis in Whiptail LizardAn all-female species

The lizard on top plays the role of a male.

They switch sex roles every 2 or 3 weeks during the breeding season, mediated by hormones.

• Parthenogenesis has been artificially induced in practically all animal phyla.

• In 1900, Jeauqes Leon did the first clear case of artificial parthenogenesis by pricking unfertilized frog eggs with a needle. He found that in some cases normal development ensued.

Artificial Parthenogenesis

• Eggs can also be stimulated to mature using things such as temperature changes, seawater solutions, and diluted acids.

• Artificial parthenogenesis is the only way parthenogenesis has been seen to occur in mammals.

• In 1936, Gregory Pincus induced parthenogenesis in mammalian (rabbit) eggs by temperature change and chemical agents.

Depending on the species, parthenogenesis happens for different reasons. Some species that normally reproduce sexually will sometimes reproduce asexually, either for lack of males, for population sex control, or in some cases because of an abundance of resources.

http://www.eba.gov.tr/ara?q=partenogenez

Natural Parthenogenesis

Artificial Parthenogenesis

It is the ability of unfertilized egg to develop into a new individual e.g. Honeybee, aphids

It is the activation of unfertilized egg to develop into a new individual artificially by exposing the eggs by heat, electric shock, radiation or pricking with a needle.  e.g. Frog, starfish, rabbit