Planet Earth

Genes are probability, not destiny

Gene ExpressionBy Razib KhanApr 5, 2012 7:53 AM


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On my Facebook feed some geneticist friends of mine were passing around an article in The New York Times, Study Says DNA’s Power to Predict Illness Is Limited. The article is based on a paper, The Predictive Capacity of Personal Genome Sequencing. In its turn this paper, as well as the write up in The New York Times, has been widely criticized in the genomics and genetics community. On the other hand, Luke Jostins cautions that perhaps one lesson statistical geneticists should take away from this is that they should do a better job communicating to the public. I'm with Luke in spirit. But I wonder:

how much more difficult is it to think in terms of probabilities rather than binary outcomes?

Because that is the ultimate issue. Even geneticists sometimes talk in "nature vs. nurture," as if the two are oil and water poured in exact ratios into a basin. Of course the reality is that nature and nurture interact, and one shouldn't discount either. Instead of talking about disease, perhaps it might help to focus on a quantitative trait like height. This is ~90 percent heritable. That is, ~90 percent of the phenotypic variation can be explained by genetic variation. The fact that Kobe Bryant's father was a journeyman professional basketball player no doubt resulted in his son's sights being set rather high in that arena. That is nurture. But as it happened, Kobe also inherited height from his father. That is nature. Talking about the two as if they are at cross-purposes misleads. Recall that height is ~90 percent heritable on the population level. But it turns out that the standard deviation of identical twin height differences is still ~35-40 percent that of random siblings! What I want to see next, an article in The New York Times: "Identical twins not always identical in height; genes don't explain everything."

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