The spread of recessive biological traits via sexual selection.

[DirtyMartini]

Originally posted by lord of the mark
Why would a recessive gene thats not evolutionarily disadvantageous be "drowned out"? Clearly the phenotype would show up less frequently then the gene, but sheer chance would mean that the phenotype would be expressed, depending on the frequency of the gene.

Exactly.

Originally posted by lord of the mark
Whats much more interesting is how clearly disadvantgeous recessive genes, ones that cause fatal diseases, survive. The candidates, IIUC, are genetic drift (sheer chance from a small founder population) versus heterozygote advantage (its good to be a carrier - the classic example is Sickle Cell Anemia and its relation to malaria - a more controversial theory (not widely accepted) is Cochrans views on Tay Sachs and other lipid/neurological conditions and Ashkenazi intelligence)

Is there any science behind Cochran's theories, or are they just pure conjecture, i.e. trying to draw a parallel between Tay-Sachs (et.al.) and malaria resistance in Sickle cell? Slippery slope IMO.

[Lorizael]

Originally posted by lord of the mark
(This post had poor genes, and failed to survive)

[Dinner]

Here's a map showing the distribution of "light colored eyes" in Europe in 1965. Notice how some areas are completely dominated by recessive traits; up to 80% or more.

[BeBMan]

I think before/without birth control rich had often large families (think about large Roman patrician clans, medieval nobles or so), but there were simply much more poor people with large families as well, so overall it's still no contest.

Also, if we go up to 0 AD, marriages esp. in rich families were often influenced by a lot of factors other than just getting young and attractive wives (like getting one with the "right" social status, from the "right" family, with best connections, political marriages etc, etc.). What is before those times (if the timeframe extends to 20k BC) where we know of such stuff I don't know.

[Dinner]

So your explanation for the frequency of recessive traits is purely the founder effect?

[LordShiva]

Originally posted by BeBro
Also, if we go up to 0 AD, marriages esp. in rich families were often influenced by a lot of factors other than just getting young and attractive wives (like getting one with the "right" social status, from the "right" family, with best connections, political marriages etc, etc.).

True.

Most queens/princesses were teh ugly

[lord of the mark]

Originally posted by DirtyMartini


Is there any science behind Cochran's theories, or are they just pure conjecture, i.e. trying to draw a parallel between Tay-Sachs (et.al.) and malaria resistance in Sickle cell? Slippery slope IMO.

Its the et al part. Its that so many of the Ashkenazi diseases are neurological, or are lipid disorders (related to neuron sheathing - maybe) etc, and which COULD be related to additional neuron connections. One interesting tidbit is that torsion dystonia sufferers (disproportionate among Ashkenazic Jews) are supposed to have higher IQs than other Ashekenazim. The IQ data itself has been questioned, and the survival rationale is the usual conjecture (he adds the interesting twist that low IQ ashkenazim, aside from possible having fewer surviving offspring, would be more likely to leave the Jewish community, where social status was so connected to rigorous religious scholarship).

http://en.wikipedia.org/wiki/Ashkenazi_intelligence

"Reviews of the controversial paper have been both positive and negative, with critics claiming the argument to be far-fetched and unsupported by direct evidence.[4] Many genetically isolated human groups have faced multifarious adaptive pressures one could cherry pick to justify currently exhibited group traits.[6]"



It definitely looks stronger than the Tay Sachs - TB connection. But the accepted view still seems to be that its all genetic drift.

Id think a very interesting study would be to investigate the IQs of Tay Sachs carriers, versus other Ashkenazic Jews, but AFAIK no ones done that.

[lord of the mark]

Originally posted by Oerdin
So your explanation for the frequency of recessive traits is purely the founder effect?

Im not sure why you think there should be ANY connection between dominance and frequency.

Think blood type.

[BeBMan]

edit: oops

[Dinner]

LotM, the mutation happened to, theoretically, one initial person and then spread from there. Some how the recessive gene has to get from one person to a dominant position in the population.

[lord of the mark]

Originally posted by Oerdin
LotM, the mutation happened to, theoretically, one initial person and then spread from there. Some how the recessive gene has to get from one person to a dominant position in the population.

In the case of the ABO blood types, the dominant genes were apparently the mutations.

Anyway, the founder effect/drift stuff depends on the size of the initial population, of course (assuming a single mutation, though Im not sure thats the case here) Big difference between one mutation in a population of 50,000, or 50, or 10. Then, the odds of drift to a larger proportion, or even a majority, are all a matter of chance, and mathematics.

Anyway, Im also not sure that lighter pigmentation doesnt have straightforward genetic advantages.

[Kuciwalker]

Originally posted by lord of the mark
(This post had poor genes, and failed to survive)

[Kuciwalker]

The recessive gene isn't necessarily the mutant one, Oerdin.

[Lul Thyme]

Re: The spread of recessive biological traits via sexual selection.

Originally posted by Oerdin
I'm interested in what people think of this theory I've been reading. It is designed to explain the spread of recessive genetic traits (examples: blue & green eyes or blond & red hair) which would normally be drowned out by dominate genetic traits (brown eyes or darker hair) in a population which was free to interbreed.

Why does this even need explaining?

That is, why should a recessive trait even be drowned out in the first place?

If Green-eyed reproduce as much as brown-eyed, the ratio of green-eyed will remain the same in the population, whether it's a recessive trait or not.

[Lul Thyme]

Originally posted by Oerdin
LotM, the mutation happened to, theoretically, one initial person and then spread from there. Some how the recessive gene has to get from one person to a dominant position in the population.

You keep assuming the recessive gene is somehow the "underdog" (has lower frequency) which is a false assumption in many cases.


Maybe the problem comes from the double use of dominant (as a trait expressing itself in the phenotype over another or as being the majority genotype in a population). Those two uses do NOT go hand in hand.