Beat frequency is bimodally distributed in spermatozoa from T/t12 mice.

Flagellar beat frequencies of spermatozoa from mice of varying genotype were studied using highspeed cinemicrography. Beat frequency was variable but unimodal in two inbred lines, their F1, and an outbred line. In contrast, beat frequency in spermatozoa from T-complex, balanced lethal stocks (T/t6 and T/t12) tended not to vary between individual males of each genotype up to four hours after collection. The two-hour distribution of beat frequency for T/t12 was, moreover, bimodal, suggesting the possible existence of two subpopulations of spermatozoa.