View Full Version : Haplogroups age need adjustment after study finds Y-DNA is evolving fast

29-01-10, 12:08
A few weeks ago, a study found that the Y-chromosome of humans and chimps differed by 30%, against less than 2% for the overall genome. The conclusion was an easy one, Y-DNA evolves much faster than other chromosomes. This came against all expectations since it was until then believed that the Y-chromosome stopped evolving in mammals and was only degenerating, shrinking in size over time compared to the X-chromosome.

Rokus posted a nice summary (http://rokus01.wordpress.com/2010/01/28/evolving-chimps-are-messing-up-y-dna-dating/) (perhaps a bit technical for the non initiated).

The consequence for population geneticists is that the current estimates for the age of haplogroups may well be wrong. If mutations happen more often than previously thought most haplogroups should be younger. It is not that simple, for two main reasons :

1) the chimps' Y-chromosome may have been under strong evolutionary pressures that did not occur in human beings, or at least not in the last 50,000 years. In that case, the current estimates could be valid.

2) there are so many Y-DNA mutations that haven't been identified yet. For example, in 2005 (http://www.isogg.org/tree/ISOGG_HapgrpR06.html) the ISOGG's tree listed only 7 mutations from R* to R-M222. In 2009 (http://www.isogg.org/tree/ISOGG_HapgrpR09.html) there were already 39 SNP's identified. There could be thousands of mutations separating haplogroups. Things will only become clear once full sequencing will become the testing standard. Prices need to fall considerably for that, but it was promised to happen for 2010. I don't think it will happen for a few more years though. Let's wait and see.

There is an important drawback with this study that I think nobody has mentioned before. The comparison of human and chimp Y-chromosomes only involved a few individuals. Chimps have a much greater genetic diversity than humans, as they did not experience all the population bottlenecks that humans did, notably during the Ice Age. A wider sampling of the chimp population will reveal big variances in the percentage of shared Y-DNA with humans. The reported divergence of 30% with humans may only be 10% in some chimp individuals, or over 30% in others. Again time will tell.