>Increased relatedness
>between parents increases the chance that the same 2 damaged alleles
>(recessive genes) will come together in their children, causing the
>disorder/defect caused by the absence of that gene product to be
>expressed.
I feel compelled to point out that not all recessive alleles cause problems
in the homozygous condition (both alleles recessive), and that some
recessive alleles, when paired with a dominant allele, actually confer
advantages to the individual -- this is true for sickle-cell and cystic
fibrosis. So I wouldn't describe them as "damaged" -- just different.
Inbreeding is not deletrerious at all in families/populations that do not
carry recessive alleles that cause problems when in the homozygous
condition.
>From a genetic standpoint, reproducing with someone as
>different as possible from you in ethnicity/country of origin is
>advantageous for your children (heterozygote superiority).
Again, I feel compelled to point out that, while it is good to reproduce
with someone genetically different from yourself, this person is as likely
to be found within your own ethnicity or country of origin as outside it.
Most human variation is found within populations, rather than between
populations.
If you have two random Norwegians who are both light-skinned, blonde-haired,
and blue-eyed, and you have one Nigerian who is dark-skinned, black-haired
and brown-eyed -- and you compare them across *all* genes, not just the few
that code for external skin/hair/eye color, the two Norwegians are NOT more
likely to be genetically closer to one another than either is to the
Nigerian. Now if the Norwegians are brother and sister, they are more
likely to be genetically closer to each other than either is to the
Nigerian, overall.
Kathy Dettwyler, ever the professor
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