The Platypus: God's Little Joke
The 1999 comedy Dogma opens with a disclaimer, exhorting the audience to remember that “even God has a sense of humor. Just look at the Platypus. Thank you and enjoy the show. P.S. We sincerely apologize to all Platypus enthusiasts out there who are offended by that thoughtless comment about Platypi. We at View Askew respect the noble Platypus, and it is not our intention to slight these stupid creatures in any way. Thank you again and enjoy the show.”
God expressed his sense of humor, of course, in assembling a creature that is a little bit mammal (the platypus, a native of Australia, produces milk and is furry), a little bit reptile (it lays eggs and has venom, released from spurs in the hind legs) and a little bit bird (eggs again, plus it has a bill like a duck as well as webbed feet). Its cognitive capacity and/or nobility we’ll leave to the guys at Dogma, but one particular platypus—Glennie, from New South Wales, Australia—has made scientists smarter: an international team of researchers from the U.S., Australia, England, Germany, Israel, Japan, New Zealand and Spain collected her DNA and from it sequenced the platypus genome, they’re announcing today in papers in Nature and Genome Research.
The platypus genome consists of roughly 2.2 billion pairs of chemical “letters,” those As, Ts, Cs and Gs that spell out a species’ genetic code. (Humans have about 3 billion.) Within those letters are some 18,500 genes, compared to maybe 24,000 in humans.
Not surprisingly, the platypus genome is an amalgam of mammal, reptile and bird DNA, too.
Like reptiles, the platypus (Ornithorhynchus anatinus) has genes for egg laying. Its venom comes from genes that are duplicates of genes that evolved in ancestral reptiles, which is also the source of venom in today’s reptiles. Like mammals, it has genes for lactation (though, lacking nipples, it nurses its young through the abdominal skin). Like birds, it has a weird way of determining sex: of its 52 chromosomes, 10 are sex chromosomes (in humans, the X and Y, of 23 chromosomes, are sex chromosomes), and the platypus X resembles the sex chromosome of birds, called Z. A female platypus has five pairs of X chromosomes, while males have five Xs and five Ys. The platypus genome contains both reptilian and mammalian genes involved in the fertilization of eggs. Unlike most mammals, which have a pretty good sense of smell, the platypus doesn’t—and its genome has about half as many odor receptors as the mouse and other mammals.
Just one request, please. In the PR avalanche preceding this announcement, one talked about the medical benefits that would surely come from this feat. ("What does this discovery mean for the public? The very real potential for advances in human disease prevention and a better understanding of mammalian evolution.") Aren't we beyond that yet? There have been virtually no medical benefits from sequencing the human genome (yet), for goodness sake; can't we, just occasionally, celebrate a feat of pure science without raising hopes that it will, you know, cure cancer or something? Sometimes a platypus genome is just a platypus genome.