Pathenogenesis and gender of offspring

All the hoo-ha over the komodo virgin birth (and I was very disappointed to read a zoo official quoted as saying, “You can be sure we won’t be naming any of the hatchlings Jesus!”), I’ve been trying to understand parthenogenesis.

And I’m not getting very far, particularly the part about what determines whether the offspring will be male or female. From the Wikipedia article about it, “Parthenogenetic populations will be all-female if two like chromosomes determine the female sex, but male if the female sex is determined by unlike chromosomes (as in the Komodo dragon), because the process involves duplication of a single sex chromosome.”

Can someone explain this to me using very small words? The part I can’t seem to get my head around is duplication of a single sex chromosome and the reference to “unlike” chromosomes. How can something duplicated result in two things that are not alike?

That bit of the Wiki article is just gibberish. Obviously, a parthenogenetic population can’t be all male!

As the article explains, the Komodo dragon has an unusual sex determination system, different from the mammalian one, in which XX is female, and XY is male. In Komodo Dragons, WZ is female, ZZ is male, and WW is inviable.

Dragons can have young both sexually and parthenogenetically. If they do so sexually, the sex ratio will be normal. If they do so parthenogenetically, one of the female’s two sex chromosomes will be duplicated, so all offspring will be male (ZZ) since WW is inviable.

If you have an all male generation, aren’t you setting yourself up for trouble in the future? Then again, probably the reason they had to go the way of parthenogenesis was a lack of males…

Thanks, Colibri! From what you’ve said, I gather the sex determination system of dragons seems to differ from other species capable of parthenogenesis. How so?

Actually, they have the same type of sex determination system as birds. Turkeys can rarely produce parthenogenetic eggs, and as in the case of Komodo dragons the offspring are all male.

I am not certain of the sex determination system in other parthenogenetic lizards, but it obviously can’t be the same as that in Dragons, since females produce female offspring (and no males at all exist in these species).