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Saturday, January 01, 2011

Y chromosome further evidence that human-chimp DNA similarity is in 70% range

Not 98% or 99%, as every motor mouth on Hoax TV can tell you, between 9-11 hair fixes.

A friend writes to say:
In 2008 I made the prediction (based on data available from the draft chimpanzee genome) that the human and chimpanzee genomes were about 70% the same overall. This has now been confirmed for the Y chromosome in a detailed study.
The study found
As expected, we found that the degree of similarity between orthologous chimpanzee and human MSY sequences (98.3% nucleotide identity) differs only modestly from that reported when comparing the rest of the chimpanzee and human genomes (98.8%)15. Surprisingly, however, >30% of chimpanzee MSY sequence has no homologous, alignable counterpart in the human MSY, and vice versa (Supplementary Fig. 8 and Supplementary Note 3).

In aggregate, the consequence of gene loss and gain in the chimpanzee and human lineages, respectively, is that the chimpanzee MSY contains only two-thirds as many distinct genes or gene families as the human MSY, and only half as many protein-coding transcription units (Table 1).
He cautions that the authors of the Nature paper do not think that their findings for the Y chromosome are true for the whole genome.

Perhaps not, but it is nice to see sane people working on genetic similarity issues for once.

The paper is: Chimpanzee and human Y chromosomes are remarkably divergent in structure
and gene content, Nature 463, 536-539 (28 January 2010) | doi:10.1038/nature08700

The human Y chromosome began to evolve from an autosome hundreds of millions of years ago, acquiring a sex-determining function and undergoing a series of inversions that suppressed crossing over with the X chromosome1, 2. Little is known about the recent evolution of the Y chromosome because only the human Y chromosome has been fully sequenced. Prevailing theories hold that Y chromosomes evolve by gene loss, the pace of which slows over time, eventually leading to a paucity of genes, and stasis3, 4. These theories have been buttressed by partial sequence data from newly emergent plant and animal Y chromosomes5, 6, 7, 8, but they have not been tested in older, highly evolved Y chromosomes such as that of humans. Here we finished sequencing of the male-specific region of the Y chromosome (MSY) in our closest living relative, the chimpanzee, chieving levels of accuracy and completion previously reached for the human MSY. By comparing the MSYs of the two species we show that they differ radically in sequence structure and gene content, indicating rapid evolution during the past 6 million years. The chimpanzee MSYcontains twice as many massive palindromes as the human MSY, yet it has lost large fractions of the MSY protein-coding genes and gene families present in the last common ancestor. We suggest that the extraordinary divergence of the chimpanzee and human MSYs was driven by four synergistic factors: the prominent role of the MSY in sperm production, ‘genetichitchhiking’ effects in the absence of meiotic crossing over, frequent ectopic recombination within the MSY, and species differences in mating behaviour. Although genetic decay may be the principal dynamic in the evolution of newly emergent Y chromosomes, wholesale renovation is the paramount theme in the continuing evolution of chimpanzee, human and perhaps other older MSYs.

Did you get that? “Wholesale renovation.” No doubt there’ll be more real news to come.

But don't expect to hear it from Hoax TV. 70%? Doesn't quite have the same ring as 99%, does it.

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