New Delhi, May 15 -- Sitting in my doctor's examination room, I was surprised when she told me, "Genetics don't really matter for chronic disease." Rather, she continued, "A person's lifestyle, what they eat and how much they exercise, determine whether they get heart disease."

As a researcher who studies the genetics of disease, I don't fully disagree - lifestyle factors play a large role in determining who gets a disease and who doesn't. But they are far from the entire story. Since scientists mapped out the human genome in 2003, researchers have learned that genetics also play a large role in a person's disease risk.

Studies that focus on estimating disease heritability - that is, how much genetic differences explain differences in ...