A
very long time ago, about 200 million years, our ancestor’s chromosomes had
developed the X and Y types that stand us in good stead today. We share a lot
of our DNA with other primate species as the species diverged about 25 million
years ago.
Us
males are very dependent on our Y-chromosomes; especially the male specific
part and over the years there has been a lot of fraying around the edges so
that we only have about 3% of the original version from 200 million years ago.
We have known about this for some time and there has been some concern that men
may be getting perilously close to their “sell by date.”
The
X and Ys started out with about the same number of genes. Currently the X has
around 800 while the Y is down to its last 78. This represents about 3% of what
it started out with, hence the tendency for us to start biting our fingernails.
To
put our minds at rest (or worry us some more) Hughes et al have sequenced the macaque genome to see if they have suffered
a similar loss (1,2). These monkey’s ancestors diverged from ours about 25
million years ago as noted above.
The
good news is that since the great divergence from the monkeys, we’ve only lost
one gene to bring us down from 79 and we’ve been keeping a firm grip on those 78 for
the past 5 million years so our male specific part of our Y-chromosome is in
good hands.
Recall
that the chimpanzees went off on their own about six million years ago and it
was in Hughes et al’s letter to
Nature (3) comparing the chimpanzees Ys with ours that started us worrying back
in 2005.
- http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10843.html
- http://www.bbc.co.uk/news/science-environment-17127617
- http://www.nature.com/nature/journal/v437/n7055/full/nature04101.html
