Bryant (
25 May 1995 22:43:44 -0600

In article <>,
Gil Hardwick <> wrote:
>In article <>, ( writes:
>>Perhaps they do so because they have noticed that the gods punish sister
>>and brother hanky-panky by sending dorked babies? <g>
>Firstly, the idealised risk of deformity is less than 1:4, assuming
>pure strains either side.

For any given deletirous recessive allele, the Mendelian ratio would be
something like that, assuming presence in only one parent. But of course
there's pleiotropic and epistatic effects to consider, too. And perhaps,
more than one nasty recessive to worry yourself with.

What, exactly, is a "pure" strain in humans, anyway?

>Secondly, even were those odds at all realistic, the couple could have
>enjoyed sexual intercourse many hundreds of times without the girl even
>falling pregnant.

Luckily, there's that Westermark Effect, disuading sibs from boinking.
Scientific American reports in the current issue that a similar mechanism
keeps gorillas from mating with those they were reared with.