Platypus Genome!

May 14th, 2008 | By | Category: Evolution


(Salim Virji)

Who doesn’t love the platypus? This is a creature bizarre enough to make marsupials feel better about themselves. The platypus, lactates (mammal!) and lays eggs (reptile!), grows fur (mammal!) and venom (reptile!).

This might be the single most interesting creature, from an evolutionary point of view, on the planet. About 315 million years ago, Amniotes–a primitive vertebrate with four legs, pretty much resembling a blurry picture of every animal that comes to mind–split into two groups. The Sauropsids eventually became all reptile-like creatures, including Dinosaurs, snakes, lizards and birds. The Synapsids became, well, us and all other mammals. Almost 170 million years ago, the Platypus split off from the rest of the Synapsids and hung out on a little evolutionary twig of its very own.

This is all a bit like reading the Silmarillion or Numbers, so I’m moving on to the big, exciting, point for evolutionary biologists. 170 million years ago, we and the Platypus shared a common ancestor. If you want to reconstruct how we evolutionarily came to have external testicles, nipples, separate opening for pee and poop–all things we have but the Platypus doesn’t–we could compare how a Platypus is put together, its genome, to our own. Our common ancestor probably lacked all these things. Likewise, the Platypus has been busy since departing our common ancestor, figuring out how do things we can’t–like make poison or see the world using only electricity. How’d that happen?

Well, we now have a draft of the Platypus genome. This’ll be fun.

Right off, the male Platypus has five X and five Y chromosomes. Huh? By comparison, every other male mammal has one X and one Y. One of the more pleasant observations is how similar we are to them. Over 80% of the genes in the Platypus strongly resemble those in humans or mice.

The remaining fifth is where all the fun actions occurs! Like what? The genes for chemical receptors, that make the nose work, are totally different. Genes for making eggs? Different from just about anything. The eggs are tiny and the baby Platypus hatches much earlier than is typical in egg-laying creatures. The baby then licks milk off the belly of the mother–remember, no nipples! If you wanted a snapshot of the evolution of mammals, that don’t lay eggs and nurse their young, this is pretty much it.

Ok, enough of my wonderment. Read the paper, if you can! If you can’t, bitch to your representative about the publication of publicly funded research in private, subscription only journals.

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