Jim Menegay wrote:

> "Anon."  wrote
in message news:...
> 
>>How can you get drift with Ne=infinity?  We've thought about it, and 
>>some have even bee into the field and sampled midlew.  It's diverse, and 
>>there's a lot of it about, so Ne=infinity is a good approximation.  I 
>>think my point is that any null hypothesis has to be referenced to the 
>>species and population you're studying.
> 
> 
> If you define "drift" to be non-selective fixation of alleles, then
> Ne=infinity seems to rule it out.  But, if you define "drift" as 
> non-selective change in gene frequencies, then you need an even larger
> population to stop drift in its tracks - you need SQRT(Ne)= infinity. ;-)
> 
> Other reasons for doubting the importance of drift in mildew are a 
> presumably small genome with little junk, presumed strong expressed
> codon preferences making even synonymous substitutions non-neutral,
> and a large ratio of haploid mitotic reproduction to sexual reproduction.
> 
Actually, the genome is large and full of crap (to put it mildly).

> It may well be that there is no significant drift in mildew, but this 
> doesn't argue that drift is an inappropriate null hypothesis.  It just
> means that, in this species, the null hypothesis is refuted.
> 
Yes, and so for any hypothesis produced now, it's not even worth 
bringing up!

My wider point was that insisting that "X should always be the null 
hypothesis" seems a bit naïve.  You'll (almost) always find cases where 
it's a non-starter, and I'd rather we thought about the specific system 
we're working with before producing hypotheses.  Context is all!

Bob

-- 
Bob O'Hara
Department of Mathematics and Statistics
P.O. Box 4 (Yliopistonkatu 5)
FIN-00014 University of Helsinki
Finland
Telephone: +358-9-191 23743
Mobile: +358 50 599 0540
Fax:  +358-9-191 22 779
WWW:  http://www.RNI.Helsinki.FI/~boh/
Journal of Negative Results - EEB: www.jnr-eeb.org
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