David Botstein, a molecular biologist who changed the course of genetics by discovering a method for locating genes in human DNA, died on Feb. 27 in Palo Alto, CA. He was 83.

Dr. Botstein began his career at the Massachusetts Institute of Technology in the early 1970s, when little was known about genes and how they interact. The human genome was understood to be a vast stretch of DNA, and the idea of locating within it any one of the approximately 20,000 individual genes that build and operate the body was daunting.

Dr. Botstein came up with the solution. The epiphany allowed scientists to find genes for cystic fibrosis, Huntington’s disease and an inherited risk for breast cancer, among many other conditions.