A genetics/population bleg

I don't know whether I have enough readers yet to start "blegging," but I thought I'd give it a shot in the off chance that one of the few visitors I do have knows something about this.

In our small group session today, one member of the group, a very liberal, biracial (black/white) young woman became reservedly yet visibly exercised when we broached the subject of genetic risk for disease being associated with race. She was quick to tell us that when working at the NIH (an experience she is obviously quite proud of--I'm sure a liberal half-black woman has no trouble getting a job at the NIH) she learned that racial risk factors, while they do exist, are really attributable to social factors correlated with race such as low income, education, living in a high-crime area, etc., rather than to genetics. Naturally, I don't buy that. She also said that the only diseases that are correctly attributable to genetics and correlate with race are single-gene disorders such as sickle cell anemia, and that even in those cases, since it's only one gene, it's not really racial since any person of any race can have that one mutation. She said that multifactorial disorders aren't really attributable to race at all, that there's more genetic variation within races than between races, and of course, repeated the ubiquitous leftist talking point that there's really no such thing as race anyway and it's merely a social construct. She made it sound like at the NIH this stuff is considered firmly established scientific fact.

Now, it doesn't surprise me at all that the NIH has "discovered" the scientific "fact" that racial differences don't actually exist, though obviously, I'm highly skeptical. But I was unable to rebut any of these claims, because I'm really not well-read on this topic, and I figured that this being a subject that is obviously near and dear to her, she would probably have several studies or articles she could cite off the top of her head which she at least believes establish her view, which would make her look like she had science on her side while I was merely a quack engaging in speculation.

So I'd like to ask if anyone can recommend good books, articles, or other sources that may show that what this woman was saying is wrong. Specifically, I'm interested in knowing more about where this idea that there is more genetic variation within races than between races comes from, what its significance really is, and whether it really means what liberals seem to want it to mean. More generally, I'd also love to know if there's been anything solid refuting this incessant claim that there's no such thing as race and it's merely a social construct.