Genetic Variation Is One of Many Factors Contributing to Health and Disease
The first human genome sequence was “completed” eighteen years ago to great fanfare,1 but even then, it was clear that that was the first step on a very long journey. Although thousands of “single gene disorders”—those in which variations in a single gene play a major role in causing disease—are known, most common diseases such as hypertension and diabetes are affected by variants in dozens to hundreds of different genes. In part because humans are a young species and in part due to the impact of history and selection, genetic variation is not distributed evenly around the world. Rather, the frequency of some variants differs depending on an individual’s ancestral origin.