The Why Behind the Y Chromosome

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Science  29 Oct 1999:
Vol. 286, Issue 5441, pp. 877-879
DOI: 10.1126/science.286.5441.877

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On page 964, two geneticists report evidence for how the Y chromosome--which is much smaller than the X--ended up so different from its partner. The researchers analyzed genes still found on both chromosomes that have remained relatively unchanged for millennia, using them to piece together a rough history of how the chromosomes drifted apart. The distinctions between X and Y didn't happen gradually, they concluded, but in a stepwise fashion, implying that at least four distinct events--most likely rearrangements of the Y chromosome--drove the chromosomes apart over hundreds of millions of years.