Doggedly searching for the crux of the biscuit.
But sharks don't necessarily have to do it.
A team of American and Irish researchers 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. [...] Scientists began their investigation after a female hammerhead shark was mysteriously born at Omaha's Henry Doorly Zoo in December 2001, in a tank that held three adult, female hammerheads but no males. [...] The team -- which included scientists at Nova Southeastern University in Florida, Queen's University Belfast and the zoo -- determined that the baby shark's genetic makeup perfectly matched one of the females in the tank, with no sign of a male parent. Mahmood Shivji -- Nova Southeastern's Guy Harvey Research Institute director and one of the paper's authors -- said that he and his colleagues 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.
A sister polar body. Doesn't explain why this never happens w/ mammals, if they know.
Posted by: I don't pay at May 23, 2007 02:00 PMA sister polar body
Are they talking about AWB?
Posted by: Clownęsthesiologist at May 23, 2007 02:25 PMum, i don't get how "the baby shark's genetic makeup perfectly matched one of the females in the tank" and yet "the baby shark['s] DNA had only half as much genetic variability as the mother."
something is missing in this story.
Posted by: Trochee at May 23, 2007 03:08 PMI think "genetic makeup" refers to natural lipstick, eyeshadow, and the like.
Posted by: M/tch M/lls at May 23, 2007 03:16 PMum, i don't get how "the baby shark's genetic makeup perfectly matched one of the females in the tank" and yet "the baby shark['s] DNA had only half as much genetic variability as the mother."
Easier to imagine from a picture of meiosis. Basically fertizilation is taking place by the combination of two of the four daughter cells. Enough for a full genetic complement, but lacks the diversity of the original parent cell.
Posted by: gswift at May 24, 2007 07:50 AMEnough for a full genetic complement, but lacks the diversity of the original parent cell.
And without an infusion of genes from a father, nearly identical parthenogically-derived lines suffer grave evolutionary threats - which is the real reason why sex evolved, as the benefit of more diversity in offspring proved to be more advantageous in passing along one's genes than simple cloning or similar tricks like this.
Posted by: TokyoTom at May 25, 2007 07:10 AMTokyoTom:
Right -- but it's even better to have the option of sexual or asexual reproduction. Stuck, like this poor shark, in an environment without males, it's parthenogenesis or nothing.
There's a quite a few insect species -- lots of aphids IIRC -- whose normal reproductive strategy is several generations of female-only reproduction for each sexual generation.
(The reasons there are a little different -- have to do with it taking several generations to fully exploit a given host plant, which might originally have been colonized by just a few individuals -- if you're going to be inbreeding anyway, might was well skip the sex. Fruit wasps that have several neotenous generations in the same fig or whatever -- reproducing in the larval form, without bothering with metamorphosis -- accomplish something similar with skewed sex rations, lots of females and just a few males, which mate with their own sisters/cousins.)
Posted by: lemuel pitkin at May 30, 2007 10:09 AM