incorygible
Posts: 374
Joined: Feb. 2006
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| Quote (Russell @ May 19 2006,12:23) | | Quote | | A somewhat greater than expected proportion of those substitutions (36% observed vs. 25% expected) are shared, suggesting the involvement of mutational hotspots. |
If you refer back to the exchange Jeannot & I had on this, I think you'll see that you don't have to appeal to anything so esoteric as mutational hotspots. The high percentage of substitutions between* rat and guinea pig sequences shared with the substitutions between* rat and human probably reflects nothing more puzzling than the fact that the rat lineage evolved rat-lineage-specific mutations in the millions of years since it diverged from the guinea pig. Unless, of course, we're talking specifically about substitutions that would result in loss of function (like missense mutations) - but I don't think we are.
(Note the careful use "between X and Y" rather than "from X to Y", since it's this thinking that somehow the rat sequence == the ancestral sequence that generates all the confusion on this point.) |
Good point -- I forgot about the rat GULO being used as the ancestral sequence. So there you go, Dave -- many of these "shared" substitutions in human and rat aren't really "shared" at all. That is, these mutations didn't happen twice (once in the human and once in the guinea pig lineage), but were present in the LCA of human, rat and guinea pig and mutated once in the rat lineage. My (and Inai's?) bad.
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