The world's weirdest animal just got weirder! A new Australian research shows that the egg laying platypuses have five pairs of sex chromosomes.
Interestingly, one of the pairs contains XX/XY system (male heterogamety) found in mammals, but another resembles ZZ/ZW system (female heterogamety)
found in birds. Platypuses with the elements of two diverse groups of animals might suggest an evolutionary link. As Jennifer Viegas from Discovery
News says, "Previously it was believed that sex systems for mammals and birds evolved completely independently from each other. If the current
research holds true, all mammals, including humans, may hold a bit of unexpected bird history from the distant past."
The weird and wonderful duck-billed platypus just got even more weird and more wonderful.
Platypuses are famous for laying eggs yet producing milk, having a bird-like bill and a skeleton with reptilian features. Now it turns out that the
mammal has an equally eye-catching way of deciding its sex, according to a study by Frank Grützner and Jenny Graves at the Australian National
University in Canberra, and colleagues.
In most mammals, including humans, sex is decided by the X and Y chromosomes: two Xs create a female, while XY creates a male. In birds, the system is
similar: ZW makes for a female, while ZZ makes for a male.
But in platypuses, XXXXXXXXXX creates a female, while XYXYXYXYXY creates a male. In other words, rather than a single chromosome pair, platypuses have
a set of ten-chromosomes that determine their sex.
The researchers worked out the make-up of platypus sex chromosomes by using fluorescent markers to stain chromosomes in platypus cells before
examining them under a microscope.
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Platypus (Ornithorhynchus anatinus
) belongs to a primate group of mammals known as monotremes. There are two other species in this group; long
and short beaked echidnas. Scientists are planning to study these members of the group also in order to see if they use the same system as platypuses.
I think this is amazing news. It would be interesting to find out if an ancestral mammal had a sex chromosomal system of ZZ/ZW.
I wonder why platypuses need so many sex chromosomes.
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[edit on 25-10-2004 by Banshee]