Neutral theory

[jbwalsh at email.arizona.edu]

Xii and Stan have brought up Kimura's neutral theory. In particular, Xi notes
that



      "For mutations which cause an obvious and significant change in phenotype,

      it is still natural selection that is mainly responsible for fixing
it (or

      not fixing it). "



Actually, since must mutations are introduced as a single copy, the chance

of it getting fixed under drift is 1/(2N) where N is the population size.

If a mutation is such that individuals carrying it have a fitness advantage

of s, then the probability of fixation from a single copy is bounded above

by 2s. While this probability is greater than 1/(2N), the punch line is

that most favorable new mutations are lost by drift during their first few

generations of existence.



For those interested, see lectures 42 - 45 for the population genetics background

and lecture 46 on the neutral theory at:



 http://nitro.biosci.arizona.edu/courses/EEB320/EEB320.html



Likewise, if you are very perverse and want to see all the gory mathematical
details, see chapters 14 - 17 at

http://nitro.biosci.arizona.edu/zbook/volume_2/vol2.html



Cheers



Bruce


 
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