him-5 is a meiotic nondisjunction mutant residing on linkage group V between
lin-25 and
egl-7. Five alleles are known, ranging in severity from 25% to 37% male progeny and up to 64% reduction in brood size at 25 degrees celsius. We have rescued
him-5 animals with a deleted version of the cosmid K02A12 (from England). Smaller fragments are now being tested for rescue. Both the Him phenotype and the ts sterility are rescued in the transformants. Broverman and Meneely observed a roughly two-fold decrease in X-chromosome recombination in
him-5, as well as in Xchromosome-specific him mutants. Our genetic analyses have shown that
him-5 is not X-chromosome specific. Using an assay which does not detect all nondisjunction events, we measured nondisjunction frequencies for Chromosomes IV and V to be 0.092% and 0.076%, respectively. These frequencies are not sufficiently large to account for the majority of dead embryos, which are mostly nullo- and quadruplo-X.