SEGREGATION ANALYSIS OF THE MOUSE RB(6.16) TRANSLOCATION IN ZYGOTES PRODUCED BY HETEROZYGOUS FEMALE CARRIERS

The segregation products in zygotes of females heterozygous for the mo use Rb(6.16) translocation were studied. Of 191 first-cleavage metapha se zygotes recovered from 16 females mated to chromosomally normal mal es, 132 were cytogenetically analyzed after sequential G- and C-bandin g. There were no products of adjacent segregation, since the six chrom osomal imbalances were unrelated to the translocation. Alternate segre gation was seen in 126 (95.5%) of the zygotes, with 85 being chromosom ally normal and 41 carrying the translocation. These results indicate preferential alternate segregation and a significant deviation from th e Mendelian 1:1 ratio (P < 0.005) for reciprocal alternate segregants, as seen earlier for males with this translocation. However, the appro ximately 2:1 ratio for normal-to-balanced segregants in females is low er than the ratios consistently seen for males. This supports the noti on that there are different underlying causes of the distortion in the sexes.