EFFECT OF SPERM GENOTYPE ON CHROMATID SEGREGATION IN FEMALE MICE HETEROZYGOUS FOR ABERRANT CHROMOSOME-1

An aberrant chromosome 1 with two large homogeneously staining inserti ons was isolated from wild populations of Mus musculus musculus. The s pecific features of the aberrant chromosome have been described elsewh ere (Agulnik et al. 1990). These include its preferential entry into t he oocyte of heterozygous females, increased mortality of homozygotes and decreased fertility of homozygous females. Here we present data in dicating that chromatid segregation in heterozygous females depends up on which sperm enters the oocyte before the second meiotic division: m eiotic drive is powerful when it is sperm bearing normal chromosome 1, and segregation normalizes during MII when it is sperm bearing chromo some 1 with the extra segment. Experimental data are adduced and expla nations offered for the observed phenomenon.