Spermatozoal Head Shape in Two Inbred Strains of Mice and Their Fl and F2 Progenies

Abstract

Seven available inbred strains of mice-A, C57, SWR, C3H, 101, CBA, and DBA-were examined for differences in the shape of their spermatozoal heads. The two most extreme strains with respect to spermatozoal head shape were found to be SWR and C57. The Fl and F2 progenies derived from crossing C57 and SWR strains were found to be roughly intermediate between the parent inbred strains. Spermatozoal head shape for these preliminary investigations was calculated as outlined by Penrose (1953). Discriminant analysis was then carried out on F2 data and a linear discriminant function was obtained whereby 13 characteristics of the spermatozoal head were combined into one "super-character" or discriminant score. The numerical value of the discriminant score was taken as an estimate of spermatozoal head shape for each spermatozoon measured. 4nalyses of variance carried out on the discriminant scores for each generation revealed that intrastrain variation was not significant in the SWR strain and reached only low levels of significance in the C57 strain. The Fl males were found to be more variable than the inbred males. A large portion of the variability between the Fl males was shown to arise from "maternal effects". The F2 males were found to be much more variable than the Fl males and an estimate of heritability was approximately 0 -9. A minimal estimate of the number of "effective factors" operating to distinguish the two inbred parent strains was found to be two. The within-male variance was found not to differ significantly from generation to generation. The implications of these results are discussed.