Re: Cromosome number changes through evolution

From: CurtAdams (curtadams_at_aol.com)
Date: 08/27/04 

Date: Fri, 27 Aug 2004 15:45:05 +0000 (UTC)

wdmorse@twcny.rr.com writes;

>Perhaps you could give a broader explanation of why "the numbers don't
>work" for chromosome changes via squeezing through in small populations. I
>ask because I think that some of the discussion of the shifting balance has
>assumed a steady state environment, ignoring the effect of events that are
>severe but (from an evolution standpoint) frequent.

Hedrick, "The Establishment of Chromosomal Variants", 1981 Evolution
35:322-332.

Basically, deleterious chromosomal variants have a slim chance of getting
through only in extremely small populations (> 100). To expect to fix even a
moderately deleterious variant, you would need repeated population contraction
to very small sizes. We know that doesn't happen often,
because it would result in neutral variation far lower than what we see.
The point is not that it's theoretically impossible but that it doesn't happen
that way in the real world.

Curt Adams (curtadams@aol.com)
"It is better to be wrong than to be vague" - Freeman Dyson

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