Y-chromosome - Will it or will it not, hold on?

Reema Narendran
Apr 28, 2012 at 11:08am IST

It was with awe and apprehension that sci-bug listened to infertility expert from Israel Dr Howard Carp say that the Y-chromosome, what makes man a man, at least genetically, is slowly on its way out of the human population.
 Dr Carp said that the degeneration of the Y-chromosome is one of the major causes of male infertility across the world. ‘’When the Y- chromosome deteriorates and carries defective genetic material to the embryo, the embryo can die and it most often results in a miscarriage,’’ said Dr Carp.
 Dr Carp had come to the city last August to take part in a scientific seminar titled ‘Advances-2011’ organised by the Trivandrum Obgyn Club as part of its annual meet.
 Once upon a time, both the X and the Y-chromosomes were of the same X shape and matched perfectly. They paired up perfectly and even used to exchange genes. That was long ago. The story goes that something terribly drastic happened and one of the two started shedding genes. This one took up the ‘Y’ shape.
 According to scientists, at the rate at which the genes were shed, it would not be long before the Y-chromosome goes completely out of existence. They gave the Y a life of just a few million years.
 The tale of the male Japanese Ryukyu spiny rats, scientifically called Tokudaia osimensis, that totally lacked the Y-chromosome, added to this fear.
 However, a recent issue of the ‘NEW Scientist’ says that this fear of the vanishing Y-chromosome may be unfounded, at least in the case of human beings. This inference comes from the work of Jennifer Hughes at the Whitehead Institute for Biomedical Research in Cambridge, Massachussetts.
 Jennifer Hughes and her colleagues very recently sequenced the Y-chromosome of the rhesus monkey, a primate that parted ways with the humans 25 million years ago.
 While the human Y-chromosome carries a mere 19 of the hundreds that it shared with the X- chromosome, Jennifer and team found that the Y-chromosome of the monkey had 20 genes that matched with its X-chromosome. What was significant was that out of the 20, 19 were the same as human Y genes. This suggests that the human Y-chromosome has lost only one gene since the human and the rhesus monkeys last shared a common ancestor.
 Jennifer Hughes is confident that the Y-chromosome, that has held steady for the last 25 million years, will continue to hold on.
 But many others working in the area do not share Jennifer’s optimism. They think if versions of the 19 genes crop up on other chromosomes, the Y-chromosome could be replaced and males might become genetically XO, rather than XY. The million dollar question is whether the human males will be able to manage without the Y as with the Y-chromosome.

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