In article <9ksf83$7li$1 at mercury.hgmp.mrc.ac.uk>,
Mingqian Huang <huang at virginia.edu> wrote:
>I have a question here:
>Deletion of a gene (just say gene A) has been found in human population
>at a high frequency. Deletion of its orthologous gene was also found in
>chimpanzees. The genomic sequences of human and chimp are very similar
>and these two deletions look just like each other. Can we say the
>deletion was inherited from the common ancestor of human and chimp or
>did it happen twice independently in the two species? Is there a way to
>tell the difference?
Suppose that the deletion alleles are all descended from a single
event in the common ancestor of chimps and humans. This leads to
at least two testable predictions:
(1) The deletion allele is old (compared to most human or chimp
alleles, which reach their common ancestors within the species).
This means that sequences near it should be unusually polymorphic.
(2) The tree of alleles should cluster the deletion alleles from
human and chimp together, rather than clustering sequences from
the same species. This could be tested using programs such as
PHYLIP or PAUP*, again based on sequences near the deletion.
The reverse of these predictions (low polymorphism, trees that
cluster within species) would suggested repeated deletion. In
that case you might want to look for unusual DNA features such
as repeats or transposons in the area--repeated DNA can lead
to deletion via improper crossing-over.
Mary Kuhner mkkuhner at genetics.washington.edu