"Ron Larson" <rlarson At umich.edu> wrote:
> I read your interesting reply to Jamie Love's question about chromosome
> 2 fusion in humans and the necessity, or lack of it, for inbreeding to
> successful mating. If there is no reproductive barrier or reduction in
> in many cases, then should it not be rather common for a species to have
> variation in numbers of chromosomes, just as there is variation in other
> characteristics that are not strongly selected against? But this does
> not seem to
> be the case.
Depends how common fusion mutations are. If they're rare, then you won't
get many of them in the population no matter what their effect is on
In any case, it's not the contention that there's *no* reduction in
fertility, just that the remaining fertility of Robertsonian fusion
mutations can in some cases be high enough to allow a small percentage of
the population to carry the mutation - which can then come to fixation if
the other factors for speciation (e.g. reproductive isolation by geographic
barriers) are in place.
You're seeing this in unnecessarily binary terms.