Sunday, May 11, 2008

Platypus? Platyplease!

As some of you may have heard, a draft of the platypus genome has recently been published. Since the platypus lineage split off about 166 million years ago, they have some features that seem pretty quirky to us eutharian mammals.

Here's a quality reproduction of part of one of the figures in the Nature paper published this week:

In case you can't appreciate my ouvre, that's a platypus (monotreme), a kangaroo (marsupial), and a rat (eutharian).

All three groups evolved from the therapsids, a mammal-like reptile from the synapsid lineage. Meanwhile the sauropsids, which split from the synapsids about 315 MYA, have evolved into birds and reptiles.

This ancient split between what eventually became platypus and what eventually became reptile is interesting because the male platypus is a venomous animal. This is already unusual and totally bad ass for a mammal but it gets better.

The genes for platypus venom come from a duplication of the beta-defensin gene family, which we all have. In fact, the venom genes in snakes and lizards also arose from a duplication of beta-defensin genes, completely independent of the duplication in the platypus lineage. That is so cool!

Another really cool thing about the playtpus is that males have five X chromosomes and five Y chromosomes and let me tell you, that's a whole lot of sex chromosomes. It still isn't clear how sex determination even works in these animals.

In case you have a spare subscription to Nature laying around and you want to see the article yourself, it can be found here. If for some reason (god knows why) you don't have a subscription to Nature but you want to read the article anyway, let me know and I'll hook you up.

And since we're on the topic evolution, here's a segment from "This I Believe" on NPR where a plaeoanthropologist talks about how she doesn't believe in evolution.

All this fills me with warm evolutionary biologist fuzzies. I don't know how somebody can look at the platypus and its ten sex chromosome and not want to know how and why these chromosomes came to be. I can't imagine not being filled with glee at the discovery that snakes and platypus got their venom in the same way.

I just can't understand how somebody could only want to know enough to stay alive and comfortable. I just can't understand how somebody can look all this, say god did it, and call it a day.


edluv said...

out of curiosity, why is the word in italicized in this sentence, "plaeoanthropologist talks about how she doesn't believe in evolution?"

Ann Thrope said...

Because she draws a distinction between believing something and believing in something.

Will Baird said...


Sorry to intrude on the blog, but...

I could have sworn that they said the sex chromosomes more closely match what you find in birds rather that what you find in therian mammals. Not being a pro bio type, I could ahve misunderstood.

Adam said...

I love your platypus rendering. It made me laugh. Thanks for that.

Ann Thrope said...

So basically the platypus X chromosome shows substantial homology with the chicken Z chromsome but not with the human X chromosome.

This suggests that the therian sex chromosomes arose after the platypus split off, especially since homologues to genes found on the human Y chromosomes are found on the (autosomal) platypus chromosome 6.

But the sex chromosomes are still designated X and Y in the platypus.

Does that answer your question Will?

Will Baird said...

Thank you, yes, it does.

Oh and I scanning through your blog, it seems I used to live down the street from you: I was on the Emeryville side of 40th street and used to walk past your apartment when I used BART regularly when I first moved from NM to Cali. How funny.

I wouldn't have stumbled on your blog except that Google Alerts is set to flag posts for me on 'synapsids.'

Ann Thrope said...

How completely random, I like it.

Small world.