Systems biology and the heritability paradox

Carl Zimmer had an essay in Newsweek a couple of weeks ago that I missed at the time: “The Gene Puzzle”. It starts with a précis of the heritability paradox: We know that some phenotypes are strongly heritable, but no single gene accounts for more than a few percent of their variation. From that, he shifts to a few hot topics in genetics, including the “microbiome” – attempts to understand the genetic interactions of the microbes that live on and in our bodies. Then to systems biology:

Research on microbes is leading scientists to think about networks of genes that interact with each other in a complex, personal ecosystem. Biologists are using a similar approach to understand how thousands of genes can work together in a single cell. They're adapting the methods of engineering, breaking these gene networks down into components that plug together, much like the components of a radio. If they can do that, they'll have taken a big step toward being able to repair our gene networks when they break down. Don't go betting your stock portfolio that all this will happen next year, or even next decade. But it's a sound wager in the long run.

I recommend the essay – it’s a nice piece for a general audience. On the other hand, I think it goes too readily from “we don’t understand this” to “it involves endless complexity.”

There’s no question that a lot of data are sitting in our genomes to be sifted through. But there’s a difference between long and complicated. Heritable traits, even if they involve many genes, aren’t necessarily genetically complex. Heritability is, after all, an estimate of the additive effects of genotypes. You can’t get any simpler than additive. Epistasis, dominance, interactions with microbial environments are all interesting topics, but it would be nice to see how far we can get by adding up the effects of genotypes.