Problems in estimating non-disjunction rate from the F-bodies of two-headed human spermatozoa.

The F-bodies of two-headed human spermatozoa offer a unique potential for estimating non-disjunction rate of the Y chromosome. But there is an unexplained quantitative discrepancy: a gross deficiency of two-headed spermatozoa with no F-bodies, relative to the numbers with one F-body in each head. Any estimation of non-disjunction rate would be overshadowed by this and other major factors. Two-headed spermatozoa cannot be regarded as a random aggregation of haploid heads in pairs. DNA measurements confirmed that each head of 25 normal-sized two-headed spermatozoa was haploid. The distribution of F-body classes is independent of whether sperm tails are single or double. Donors with an exceptionally high incidence of two-headed spermatozoa exist.