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Study: Recent Selection in Many SNPs

  1. Dec 23, 2005 #1

    selfAdjoint

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    A big new hapmap study has concluded that there has been strong recent selection (indicated by significant decay of linkage disequilibrium) in over 1800 gene-sites.

    http://www.pnas.org/cgi/reprint/0509691102v1

     
    Last edited: Dec 23, 2005
  2. jcsd
  3. Dec 23, 2005 #2
    Did you see the article about a month ago that specu;ated that human-chimp differences may be more a result of inversions, than actual DNA sequence differences?

    This is not directly related to snrps (which I assume are the same as SNP's) but on the other hand if you like the one, you probably dig the other.

    http://www.sciencedaily.com/releases/2005/10/051026081736.htm

     
  4. Dec 24, 2005 #3

    Monique

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    Interesting study, I like the approach they've taken.

    I don't understand your comment though that a significant decay of LD (linkage disequilibrium) would indicate selection. They base their results on the fact that a novel allele would be lost quickly in a population and that old alleles have small LD blocks. A high frequency allele with a large LD block must thus be caused by positive selection (or the other causes they mention: inversion, bottleneck, admixture).

    They do mention progressive decay specifically on page 136, where I think they distinguish between linear decay (no selection) and exponential decay (selection) because as they say "the number of possible meiotic recombinations not eliminating the advantageous allele increases as a function of distance from the selected site", which make sense.

    For those not familiar with the term linkage disequilibrium: you have equilibrium when you can NOT predict the neighbouring state of a marker, since they are in equilibrium the state is 'random'. You have DISequilibrium when you can predict the state of a marker by knowing the state of its neighbour.

    An example when this happens is when the chromosome has a common ancestor: the states of all markers will be the same on the whole chromosome. Since recombination happens (about 40 per meiosis) this linkage disequilibrium decays because markers are exchanged between chromosomes. When there is linkage disequilibrium, marker states are inherited together (no recombination took place).
     
  5. Dec 24, 2005 #4

    Monique

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    That's interesting..
    The only definition I know for SNRPs are small nuclear ribonuclear proteins, which make up a complex splicing machine that removes introns from RNA, not related to this.
     
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