Credit: Wikipedia
Weird mammals, weird results
If the platypus sex chromosomes are not similar to ours, then what are they like? To use the words of the eminent geneticist Jenny Graves at Australian National University in Canberra. When it to comes to sex determination "platypus do it like a chook".
She says that because work from her lab and others at ANU, has revealed that the platypus sex chromosome is very much like the big sex chromosome of the bird – the Z. "In the past we identified a handful of genes that were the same; now its clear that the platypus X-5 and the chcken Z, share hundreds of genes; they're virtually the same [chromosome]."
For many researchers this is totally confounding. Birds and platypus are on very different branches of the evolutionary tree.
But Graves suspects their common ancestor may well have had both systems of sex determination: XY and ZW, and that their offspring may have opted for one way or the other, or even both. It was she says, "not supposed to be able to happen". But the Japanese frog Rana rugosa, shows it can happen. Some populations are XY; others are ZW.
"When you work on weird Australian mammals you get weird results, and these sometimes have tremendous consequences," says Graves.
It seems, two hundred years on, the platypus is still causing upheavals. But only the first few pages of the ancient platypus text have yet been decoded. With scientists around the world immersing themselves in this and other animal genomes, they hope that the the long-buried secrets of mammalian evolution will gradually emerge.
Elizabeth Finkel is a Melbourne science writer, a contributing editor of Cosmos and the author of Stem Cells: Controversy on the Frontiers of Science.
fascinating
so what happends if there arent a complete transfer of 5 chromosomes?
like 6 x's and 4 y's ?
is the 5 transferred as a package?
is information on the y equivalent chomosomes dominant over each other?
are they duplicates or are they different?
so many more questions
Eliot
platypus sex chromosomes
Hi Eliot,
good questions. You would not get offspring if the platypus had not worked out to sort out the ten sex chromosomes and we showed that it works reliably (Grutzner et al. 2004, Nature). How they do it? The all stick together in a chain of chromosomes X1Y1X2Y2....X5Y5, then all Ys wander off in one direction and all X in the other (in a way it is as a package), how they do it? We don't know,
The chromosomes are not duplicates they all carry different genes.
Cheers, Frank.
Platypus genome
Excellent article, marred only by the common practice of journalists to confuse 'code' with 'information'. With minor and rare exceptions, the genetic code is universal, being the same for cabbages, mushrooms, jellyfish and camels. Just as it was possible to transmit an infinite number of messages using the Morse code, the genetic code makes possible a virtually infinite variety of proteins.
Martin Hanson, retired science teacher