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View Diary: "Y-Chromosomal Adam" possibly farther back in time than thought (237 comments)

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  •  Fusions are quite common actually (1+ / 0-)
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    Evolutionary biologists look at something called synteny to infer where chromosomes came from.  A simple example:

    Chromosome 1 from humans has genes A, B, C
    Chromosome 1 from chimps is also A, B, C
    this would suggest these two chromosomes have not undergone any large change since our last common ancestor

    Chromsome 2 from humans has genes D, E, F, G, H
    Chromosome 2 from chimps has D, E, F
    Chromosome  3 from chimps has G, H

    this would suggest that either our last common ancestor had 1 chromosome that split (we were ancestral) our 2 chromosomes that fused (chimps were ancestral).  The reason its believed to be a fusion is that our chromosome 2 has remnants of a second centromere (should only be 1 per chromosomes), as well as remnants of telomere repeats (which normally are on the ends of chromosomes).  

    These large changes of structure happen a lot over evolutionary time, and are called gross chromosomal rearrangements (GCRs).  

    PZ Myers at Pharyngula has a really nice discussion on synteny, and has a picture at the bottom of the post of how human chromosomes match to puffer fish; large blocks of the puffer fish chromosomes are still intact, but in human chromosomes, they've been scattered all over.

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