Female Sharks Can Reproduce Alone

mikesd81 writes "The Washington Post has an article about a team of American and Irish researchers that have discovered that some female sharks can reproduce without having sex, the first time that scientists have found the unusual capacity in such an ancient vertebrate species. Their report concludes that sharks can reproduce asexually through the process known as parthenogenesis (the growth and development of an embryo or seed without fertilization by a male). Scientists started investigating after a female hammerhead shark was mysteriously born at Omaha's Henry Doorly Zoo in a tank that housed 3 female sharks. It was originally thought one had stored sperm from a male shark before fertilizing an egg. However, baby shark's genetic makeup perfectly matched one of the females in the tank, with no sign of a male parent."

Comments

Parthenogenesis does not create a clone

[Anonymous Coward]

the baby should not have been genetically identical to anything in the tank unless its mother was also a parthenogen. parthenogenesis creates a homozygotic offspring that can have any random mix of the two chromosomes the mother carries for each pair. so if the mother has AB, the parthenogenic offspring can have either AA or BB, which is not identical to the mother since the mother has AB. the only way it can be identical is if the mother is also homozygotic and therefore a parthenogen.

Re:Parthenogenesis does not create a clone

[ozborn]

determined that a byproduct formed when sharks produce eggs, known as a sister polar body, had fused with an unfertilized egg to produce the baby shark, whose DNA had only half as much genetic variability as the mother.

You've misread the article (which in fairness was not precisely written) and you're misunderstanding how parthogenesis is working here. The article claims only that the offspring is a perfect genetic "match" for the mom, not that it is identical to the mom since it also says the offspring has half the variability. What this means is the genetic test they did not pick up any polymorphisms not found in the mother. That's what they mean by "identical match".

Also parthogenesis does not create homozygotic offspring (although given enough generations it will), the immediate offspring is a result of a fusion event between 2 products of meiosis - the egg and one of the polar bodies. Thus the offspring will have a different genetic makeup to the mother. In particular half (on average) of the mother's heterozygous loci will become homozygous in the offspring. Thus the offspring has half the genetic variability.

This has potentially bad consequences because of the # of recessive lethal alleles the average organisms carry. Think of parthogenesis as the worst form of incest possible.

Great Whites?

[JRGhaddar]

This is actually really interesting, and makes a lot of sense. Shark's genetics haven't evolved that much from its ancient relatives so this reproduction method would definitely limit variations. But I am curious as to if this is how the great white reproduces. Very little is known about the great whites breeding habits. One of the prevailing theories centers around whale carcasses.