Geneticists are uncovering another level of human ethnic diversity: It may not be which genes we have so much as the way they behave that accounts for our differences. Using the International HapMap Project, which catalogs human gene variants across populations, University of Pennsylvania researchers Vivian Cheung and Richard Spielman first collected the gene sequences of a particular white blood cell from 82 Asians and 60 people of European descent. Then, using microarray chips, they measured expression levels of those genes.
What they found was surprising: Although which genes were present didn’t differ dramatically between the Asians and the Europeans, their expression did. And that expression was governed by single nucleotide polymorphisms (SNPs)—one-letter changes in DNA—in nearby regulator regions that determine how much of a gene’s product is made. Overall, 25 percent of the genes seem to show different levels of expression in Asians versus Europeans, and SNPs in regulatory regions probably account for much of the difference. In the case of one gene, researchers found that Caucasians expressed it at 22 times the strength that Asians did.
All this is important not because of what it tells us about traits like hair color but because it will help explain why certain ethnic populations are more susceptible to complex, gene-influenced diseases like hypertension and type 2 diabetes mellitus, says Cheung. Differences between populations in gene expression have not been well characterized before. “This should allow us to identify genetic reasons why some diseases are more common in one population than in others,” she says.