Irving Gottesman, a pioneer in the field of behavioral genetics whose work on the role of heredity in schizophrenia helped transform the way people thought about the origins of serious mental illness, died on June 29 at his home in Edina, Minn., a suburb of Minneapolis. He was 85.

His wife, Carol, said he died while taking an afternoon nap. Although Dr. Gottesman had some health problems, she said, his death was unexpected, and several of his colleagues said they received emails from him earlier that day.

Dr. Gottesman was perhaps best known for a study of schizophrenia in British twins he conducted with another researcher, James Shields, at the Maudsley Hospital in London in the 1960s.

The study, which found that identical twins were more likely than fraternal twins to share a diagnosis of schizophrenia, provided strong evidence for a genetic component to the illness and challenged the notion that it was caused by bad mothering, the prevailing view at the time.