James F. Crow, a leader in the field of population genetics who helped shape public policy toward atomic radiation damage and the use of DNA in the courtroom, died Jan. 4 at his home in Madison, Wis. He was 95.

The cause was congestive heart failure, his daughter Catherine Rasmussen said.

Population genetics uses mathematical and statistical methods to understand evolutionary change. Crow was a leading exponent of the subject for more than half a century at the University of Wisconsin-Madison. He was the author of two leading textbooks on the subject, one of them written with Motoo Kimura, a prominent Japanese geneticist and former student.

The methods of population genetics have emerged as the principal tool for exploring the genetic roots of disease and for interpreting the torrent of data now flowing out of the human genome project, the effort to determine the complete sequence of DNA in human chromosomes.

Beyond the campus Crow was an influential figure in addressing major issues of genetics and shaping public policy toward them.

“He was the real organizer of population genetics in the United States,” said Will Provine, a historian of biology at Cornell University.

Crow served on a genetics committee set up by the National Academy of Sciences to assess mutational damage in those exposed to radiation from the atomic weapons dropped on Hiroshima and Nagasaki.

Until 1972 he led the academy’s effort to provide genetic advice to the government on vexing issues like the above-ground testing of nuclear weapons and the effects of low levels of ionizing radiation.

The academy’s concern about above-ground nuclear explosions was a significant factor in the eventual ban on such tests by the United States and other countries.

The damaging effects of radiation fit with Crow’s academic interest in mutational load — that is, the accumulation of changes to DNA, most of which are deleterious. In 1979 he was chairman of an academy committee on the mutational effect of environmental chemicals.

Crow led still another academy committee on the forensic use of DNA. Its reports in the 1990s helped legitimize the use of DNA testing by the courts.

“When the National Academy of Sciences wanted an exemplary report lucidly written and completed on time, it always called on Jim to chair it,” Seymour Abrahamson, a colleague of his at Wisconsin, wrote in this month’s issue of the journal Genetics.

Crow’s long career traced the history of population genetics. He was well acquainted with two of its three founders, R.A. Fisher and J.B.S. Haldane, and he invited the third, Sewall Wright, to his department at Wisconsin after Wright retired from the University of Chicago.

The importance of population genetics’ methods was for many years not so apparent. Daniel L. Hartl, a geneticist at Harvard, wrote in a recent article that as a graduate student he had once asked Crow if he could join his lab. “Yes, Dan,” Crow replied, “provided you understand that population genetics is a recondite field that will never be of great interest except to a small group of specialists.”