The Rapidly Evolving Y Chromosome
Dave Greenfield | Date: 02-05-10 | Comments: 2
- A new study shows that Y chromosomes might be evolving faster than expected, but that has yet to take men off of Venus.
Six million years is a mere blip on the screen of evolution,
but a blip long enough to separate man from chimpanzee. A study headed by David
Page of the Whitehead Institute has found that the key that separates men from chimps
may be in the Y chromosome, at least partly. Dr. Page’s team found that man’s Y
chromosome is evolving much faster than expected, refuting the belief that man
and chimp Y chromosomes were very similar.
Painstaking sequencing of the human Y chromosome was completed
in 2003 by the Genome Center
at Washington University
after 13 years of work, and Page’s team took eight years to sequence that of a
24-year-old chimp. They were then able to compare the structure and gene
content of each, with unexpected results.
For half a century, it was thought that the Y was in a state
of decline, or at least stagnation. Why? It is seen as a single genetic unit,
rather than a series of blocks that can be interchanged. A mutated gene can be
swapped for a good copy on its chromosomal pair, except between the X and Y. If
this happened, it would create gender ambiguity. Because of this inability to swap, most of the genes on the Y
chromosome have decayed. Two hundred million years ago, the Y had the same
genetic material as the X, and most have now disappeared. Most scientists saw
this as evidence that the Y chromosome was either headed for eventual
extinction or was stagnant.
Page’s team found, instead, that the Y is constantly
evolving—and faster than any other part of the genome. Most of man’s genome is
99 percent identical to chimpanzees, differing in some cases only by a single DNA
unit. The Y chromosomes of the two species, however, differ by 30 percent,
indicating rapid change in the time when man and chimp split from a common
ancestor. Instead of decay, they found renewal. Dr. Page says, “Natural
selection is shaping the Y and keeping it vital.”
How does the Y’s rapid change affect the human genome as a
whole? Dr. Page says it is “hard to imagine that these dramatic changes in the
Y don’t have broader consequences.” What those consequences are is as yet
unseen, but one thing it does not mean
is that men are evolving faster than women.
