rufio wrote:No, but I know that sickle-cell is a trait that is only supported in parts of Africa where malaria is a definite danger, and not in the US. As a genetic trait, it would tend to get weeded out throughout generations of interbreeding of people who did not come from that area of Africa and do not have that trait.-
This is incorrect. The SCA mutation will continue to be passed down over time. I agree that its penchant for causing illness would lead to it to literally "die out" of the population if we all lived on the savannah. This is not the situation with modern medicine. SCA crisis is a routinely treated event in most EDs in cities with large AA populations. Thus the population that would die from extremely severe SCA crises survives and reproduces. Therefore the SCA trait tends to spread throughout the AA population. Your reasoning is sound, and is well grounded in population genetics theory, but in humans, population genetics theory is routinely trumped by technological advances.
Now, the assumption that over time and by breeding with a large reproductive pool a trait is "weeded out" is incorrect. I realise this makes intuitive sense, but as with so much in biology, intuitive sense leads to wrong anwers (trust me on this one, the only "C" in my bio career was in general genetics!
). Instead, over time the trait is dispersed into a population. Thus the SCA mutation is now present in people whose ancestors were probably not part of the original population from whence the mutation sprang. Indeed, SCA has been observed to be increasing across all racial types as the silly prohibitions against miscegenation have dissapeared.
Therefore, short of introducing Hitlerian eugenics programs,or withholding care from patients in SCA crisis, the SCA trait is unlikely to ever dissapear from the population.