born Nov. 21, 1891, Jacksonville, Ill., U.S.
died April 5, 1970, Pasadena, Calif.
U.S. geneticist.
He received his Ph.D. from Columbia University and taught principally at California Institute of Technology (192870). In 1912 he developed a technique for mapping the location of specific genes of the chromosomes in Drosophila . He later proved that crossing-over (the exchange of genes between chromosomes) could be prevented in Drosophila . He was one of the first to warn against the hazards of fallout as a consequence of nuclear bomb testing.