Sister chromatid exchanges: a reexamination of the evidence for sex and race differences in humans.

Published evidence for human sex and race differences in sister chromatid exchange (SCE) levels is reexamined. There is substantial support for the conclusion that women average approximately 0.5 SCE/cell higher than men among normal healthy adults. An index of heterogeneity for SCE counts for cells from a single subject is introduced, and this statistic is applied to the data of Butler [1981], who compared Caucasians, Blacks, Native Americans, and Orientals with regard to SCE levels. There is evidence in Butler's data of differences in the heterogeneity index among these four racial groups, but this finding needs independent verification in a larger study.