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Rare variants and human genetic diversity

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Sigbold
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10 Jul 2012, 11:46 pm

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You may have read that there is more genetic variation within major ethnic groups than between ethnic groups. That this precludes the possibility of group differences is Lewontin's Fallacy (explained in pictures).

Deep sequencing of the human genome, which reveals rare variants (here, defined as those found in fewer than 0.5 percent of the population), shows that there is actually more variation between groups than within groups. (So what you may have been taught in school is not true -- sorry, that's how science works sometimes.) The figure below, from this July 6 Science article, shows that over 50 percent of rare genetic variants are found in African populations (which have greater genetic diversity) but not in European populations. About 41 percent of all rare variants are found only in Europeans and not in Africans, and only 9 percent of the variants are common to both groups.

These rare variants are likely recent mutations. Unsurprisingly, they differ in populations that have been geographically separated for tens of thousands of years.

(...)



biostructure
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11 Jul 2012, 12:07 am

Interesting. I had heard of the idea that the majority of phenotypic heritability (and so probably variability too) is due to rare variants, and I had heard of the whole argument that genetic variation is not split along racial lines. I didn't know that one of these could refute the other.

Though I do wonder what happened to the Asian populations there, and all the indigenous tribes from somewhere other than Africa... I'm thinking that they meant to say "over 50 percent of all rare variants found in Africans or Europeans are unique to Africans".



one-A-N
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11 Jul 2012, 12:14 am

Yes, the greatest genetic diversity is found in Africa, and it reduces the further from Africa you get.

That is really not surprising. Only a subset of Africans moved into the Middle East. Only a subset of those Middle Easterners moved into Europe, and a different subset into Asia. A smaller subset again of the Asians moved into the Americas. Every time a subset breaks away into a new territory, its gene pool is smaller than its parent population's gene pool - because they leave some of the genetic varieties behind in the people who do not move on. So when you get to the bottom of South America, there is greatly reduced genetic diversity.

The only real qualifications I can think of, that should be added here are: (1) new mutations in the migrating groups, and (2) meeting and interbreeding with older populations (Neanderthals, Denisovans) in those non-African regions.



ruveyn
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11 Jul 2012, 8:53 am

How much genetic variation will there be between groups. Because of technology there are no longer any real geographic barriers to human mating.

ruveyn



Oodain
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11 Jul 2012, 10:39 am

as far as i can tell it says european-americans and african americans, not europeans adn african.

so he has used a subset within a subset to make conclusions andout all sets.


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LKL
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11 Jul 2012, 6:44 pm

ruveyn wrote:
How much genetic variation will there be between groups. Because of technology there are no longer any real geographic barriers to human mating.

ruveyn

this is an important point. Two blond, blue-eyed parents can have a sickle-cell child in the US, or one with cystic fibrosis (conditions that originated and that mostly occurr in Africans and Ashkenazi Jews, respectively). The shuffling of genes is the entire reason that sex exists, and over many generations all of these rare variants are going to be mixed and matched; the ones that work (ie, produce grandkids) will tend to proliferate, and the ones that don't will tend to die out.