If a gene occurs in 0.1% of the population, wouldn't the chances of it being unmasked by random mating be one in one million?
0.1%=0.001
(.001)(.001)=.000001

Razib doesn't mean 0.1% have the gene, but 0.1% have recissive disorders. For instance about 4% of peopple of European descent carry the cystic fibrosis allele. A child needs to inherit both recissive alleles to get the disease. This occurs in about 0.04% of the population.

no, i did goof the multiplication!

What about the problems caused by outbreeding depression?

Is there any evidence of such problems Ahrimahn? I have not seen any. Unless you mean hybrids.

Weird parent-child gene conflict possibility. If paternal investment is zero, and the selective fitness of the children of half-siblings is between .5 and .66 it is in the parent's interest for any daughters to be impregnated by their half-siblings or their "that-parental-side" uncles. The math is easy here, but can be extended to include a parental interest in mating their daughters with any absentee father who is more closely related to them than to the daughters, and to include cases with some paternal investment. Biological basis for resistance to parental mate choice? This is also a conflict of interest between the parents, and assuming they each have some ability to realize their preference can be a prisoner's dillemma.

What about the problems caused by outbreeding depression?

assumed to be minimal within species, though that depends. in frogs, which are often highly inbred, extremely patchy in distribution and philopatric, outbreeding depression is an issue, but remember that even a minimal amount of migration can work against divergence in allelic frequencies. and fitness is a net effect. positive genetic correlations are broken up by sexual reproduction, but overall the benefits are worth it over the long run. usually the same in regards to outbreeding within many species, though if you are really curious about this topic, please look at plants, who have a host of selfing and non-selfing mating regimes.

But if you're looking at the effect over many generations rather than just one, shouldn't all this cousin-marrying lead to these fatal recessives becoming much less common and eventually eliminated?

It seems to me that if people just marry at random, that means the selection penalty for carrying a fatal recessive is inversely proportional to its frequency in the population, and that means once the frequency gets below 1% or so it'll mostly just change by genetic drift. But if everyone marries a cousin, then if you have a fatal recessive then there's a 1 in 4 chance your cousin wife has it also, hence a 1 in 4 chance of it being expressed in your doomed offspring, so the frequency of (all) fatal recessives ought to reliably fall by a factor of 15/16 every generation.

shouldn't all this cousin-marrying lead to these fatal recessives becoming much less common and eventually eliminated?

yes, inbreeding should purge genetic load. this doesn't seem to work well for complex animals though, at least the empirical studies suggest that it doesn't. it does tend to work well for selfing-plants.

Is there any evidence of such problems Ahrimahn?

Mixed-race students report more troubles

"Genetic Find Stirs Debate on Race-Based Medicine"

Dr. Stefansson said he believed that the more active version of this gene might have risen to prominence in Europeans and Asians because it conferred extra protection against infectious disease.

Along with the protection would have come a higher risk of heart attack because plaques that build up in the walls of the arteries could become inflamed and rupture. But because the active version of the gene started to be favored long ago, Europeans and Asians have had time to develop genetic changes that offset the extra risk of heart attack.

The active version of the inflammatory gene would have passed from Europeans into African-Americans only a few generations ago, too short a time for development of genes that protect against heart attack, Dr. Stefansson suggested.

1) the first point is dumb for obvious reasons, there are no necessary genetic implications (some populations are by definition mixed-race genetically, but they don't identify as such). if you are new to this blog, please be aware of this. we have some standards.

2) the second one is more interesting. and it isn't surprising seeing from what i've read in regards to epistasis in aterioscerlosis from alan templeton.

3) that doesn't obviate the reality that inbreeding depression is a particular problem. there are multiple levels of population substructure.

4) there isn't one elegant vector that defines fitness. you have to sum over multiple parameters, and take into account context. and frankly, even the fitness equilibrium varies by environment. the article you pointed to would be irrelevant 200 years ago because most people didn't make it to the point where they could die of heart attacks, on a pure reproductive level it is likely not a big deal since most people reproduce before they start becoming at risk for ateriosclerosis.* of course, quality of life is an issue, we care more than about reproduction.

5) one implication of mixing racial backgrounds might be increased range in fitness because novel positive and negative combinations. synergistic epistasis, one argument for sex in general.

6) both the theory and data really aren't deep enough on this topic in regards to humans to come to a specific conclusion (i.e., a prediction equation where you plug in genetic distance numbers that pops out fitness of offspring).

7) if you are a white nationalist, please don't post again. if you aren't, no problem.

* and i suspect most genetic incompatibilities will be found later in life because of antagonistic pleiotropy.

and to be precise on #6, we have a much better (though imperfect) grasp on inbreeding depression than we do on outbreeding depression in mammals (we know about outbreeding depression in plants, amphibians, etc. more from what i can tell). so that's why 'what about outbreeding depression' can't say much. you can go do the research yourself of course :)