Thursday, December 21, 2006

Leaping Lizards.

Must be the time of year but the finding of Komodo Dragon females that are able to produce young from unfertilized eggs has really caught on as explained in this article from the Independent:

http://news.independent.co.uk/uk/this_britain/article2091881.ece

Some articles have referred to what's going on as virgin birth but who really knows if the lizard was a virgin or not? Oh different use of the word. See for instance:

http://www.teambio.org/2006/12/virgin-birth-authenticated-babies-expected-around-christmas/

In humans, were this sort of reproduction to happen, the offspring would be female since the sex chromosomes are different size wise in males which typically have one X and Y chromosome. In Lizards apparently it is the female that has two different sex chromosomes.

So if the female produces a zygote by parthenogenesis the resulting offspring will be male according to the article. The Komodo uses a so called WZ sex determination system. WZ zygote develop into females, WW zygotes into males and ZZ zygotes are inviable. No females are produced by the parthenogenic Komodo lizards because the form of parthenogensis used involves a duplication of the female lizard's chromosomes in the gamete. So the diploid "zygotes" are either WW or inviable ZZ.

There are other parthenogenic lizards, the best known being some whiptail lizards such as the ones described here:

http://fireflyforest.net/firefly/2005/11/28/sonoran-spotted-whiptail/

In these lizards the offspring are all female. This is apparently because in these lizards, in contrast to the Komodo dragon, the females have two identical chromosomes size wise, the lizard equivalent of the 'XX' chromosomes of human females. See

Modi and Crews. Current Opinion in Genetics & Development 2005, 15:660–665
http://cluster3.biosci.utexas.edu/faculty/lizard/public/Modi_Crews.pdf

These lizards exhibit pseudocopulatory behavior where one female will mount another. Here is a movie from David Crew's website:

http://www.utexas.edu/research/crewslab/oldweb/movies/cnemi.mov

One lizard takes the male role the other the female role. This behavior has the effect of stimulating both lizards to ovulate.

As for humans and the Virgin Birth of Christ, it seems you have 4 choices:
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