Comment by ocfnash | Hacker News Reader

Comment by ocfnash | Hacker News Reader

Just recently I learned that Komodo dragons have the unusual feature of being able to reproduce via parthenogenesis. This means that a female dragon, can become pregnant spontaneously!

Apparently the cell which grows into the baby dragon is formed from an ordinary egg cell that duplicates each of its chromosomes rather than having a second set of chromosomes provided by a male sperm cell, as in sexual reproduction. It turns out that the Komodo sex determination system means the offspring are always male.

I believe this means that the offspring are thus completely homozygous, though not clones of their mother because the egg chromosomes were formed by the usual meiosis. Even more amazing (I think) is that there are apparently some boa snakes which can also reproduce via parthenogenesis but whose sex determination system makes all offspring female. IIUC, if any of these daughters were also to reproduce via parthenogenesis, then their offspring would indeed be clones of their mothers. A sort of genetic end point.

This occurs in other snake species as well, the documentation is not always complete, but there is evidence for adders and pythons.

> It turns out that the Komodo sex determination system means the offspring are always male.

Do you mean when it is not parthenogenenis? How does this work?

EDIT: these are some of the snakes that I think it has been (partially) documented for:

Copperhead

Fur de Lance

Some types of rattlesnakes

Burmese Pythons

Reticulated Pythons

>> It turns out that the Komodo sex determination system means the offspring are always male.

> Do you mean when it is _not_ parthenogenenis? How does this work?

I mean all Komodo offspring produced by parthenogenenis are male even though offspring from usual sexual reproduction in Komodos can be either gender. The reason is that the Komodo sex determination system is logically opposite to that of mammals. Specifically, whereas in mammals, a pair of homologous sex chromosomes XX, produces a female, in Komodos this produces a male, ZZ. (Parthenogenenis means there is also the possibility of Komodo WW embryo but these are not viable.)

Happy to hear someone else thinks this is interesting.

Ah, so it is the same symbols as with birds.

So that means that the female will have ZW, but it would double its Z_1 and give its offspring Z_1Z_1?

Reply on news.ycombinator.com