Recently read an article about a komodo dragon that became pregnant without the presence of a male (parthenogenesis). However, the article stated that the offspring were not exact clones of the mother. How is that possible? I thought that in parthenogenesis, an egg would be created by mitosis, rather than meiosis – but that would make it genetically identical to the germ cells of the mother… so how does this happen?
Heres the article: http://www.msnbc.msn.com/id/16784022/
Parthogenic offspring will in general have less genetic diversity than the mother. As I understand it, while the mother will (presumably) have two distinct genes for each gene locus, the offspring will either have only one, or will have two copies of the same one. So the offspring might, for instance, express recessive traits for which the mother was only a carrier. Now, if the mother was herself the result of parthogenesis (not possible for komodos, but possibly for other species), then, yes, any parthogenic offspring she in turn has would be identical to her.
Do you know how the zygote (i guess not the proper term in this case?) would form? would an egg form from mitosis? (in that case, why is the young not identical?) or would two eggs somehow combine their genetic contents as a sperm and egg normally do?
I looked at various sources, which verified that parthenogenesis doesn’t create clones. But none said exactly why. I think I remember from college biology, so here goes.
The initial cell undergoes meiosis, which creates two haploid (single-set) cells. These then copy their haploid set to become diploid cells, able to then progress to become viable individuals. That’s how siblings of parthenogenesis are unique individuals, and also different from their mother.
For example, if one particular gene pair in the mother is JK, her initial cell will have this. When it meiosises, one haploid has J, the other has K. These then copy their haploid set to become diploid: the J haploid becomes a JJ diploid and the K haploid becomes a KK diploid. Neither is the same as its sibling nor its mother.
Now, if the mother is a parthenogen (a child of parthenogenesis), then all her diploid pairs of chromosomes are matched pairs. So if she reproduces parthenogenetically, all her haploids will be identical to each other. Once they become diploid, they’ll be exact copies of their mother. A KK mother will make 2 K-haploids. These then copy their haploid set to diploid, making two KK-diploid individuals, a copy of their mother.
In the case of the Komodo dragon, all the parthenogens are males. In Komodos, the sex chromosomes are W and Z. A WZ is a female and a ZZ is a male. The diploids that are created are either WW or ZZ. But WW individuals are not viable, so only ZZ males are born.
(If humans could do parthenogenesis, all the parthenogens would be female. Females are all XX, so the haploids would all be X, becoming XX-diploids.)
Got it. That makes sense. Thanks!
You can look to western Australia for other examples of parthenogenesis. The desert areas have had particulary nasty UV and high temperatures for years now. The rate of parthenogenesis has increased dramaticaly in some lizards, snakes and plants. The stress of the harsher conditions seems to trigger this. This is a problem when it’s occurring to most animals of a species over a long time in an area. They can all die at once because of a disease.
Cool! Glad I explained it well.
Getting blank stares from my trig students sometimes makes me wonder if I can correctly explain anything anymore. 