Effect of sperm genotype on chromatid segregation in female mice heterozygous for aberrant chromosome 1.

An aberrant chromosome 1 with two large homogeneously staining insertions was isolated from wild populations of Mus musculus musculus. The specific features of the aberrant chromosome have been described elsewhere (Agulnik et al. 1990). These include its preferential entry into the oocyte of heterozygous females, increased mortality of homozygotes and decreased fertility of homozygous females. Here we present data indicating that chromatid segregation in heterozygous females depends upon which sperm enters the oocyte before the second meiotic division: meiotic drive is powerful when it is sperm bearing normal chromosome 1, and segregation normalizes during MII when it is sperm bearing chromosome 1 with the extra segment. Experimental data are adduced and explanations offered for the observed phenomenon.