Download
1 / 14
250 likes | 1.56k Vues
PARTHENOGENESIS parthenos "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.
E N D
PARTHENOGENESISparthenos "virgin" and genesis "creation" Reproductionwithoutfertilization
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 eggwhich is a specialized reproductive cell.
Parthenogenesis In what organisms does parthenogenesis occur? • Occurs in many types of plants • Invertebrateshoneybees, aphids, ants, some scorpionsandmany others • Few vertebrates komodo dragons, mole salamenders, hammerhead sharks, some reptiles, some amphibians, some fish, rarelyin birds • Can be artificially induced (even in mammals)
Parthenogenesis in Honeybees Honey 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.
Parthenogenesis in KomodoDragons A baby Komodo dragon hatches from an unfertilizedeggat 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 WhiptailLizard An 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.
Artificial Parthenogenesis • 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.
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.
