DOUBLE OR NOTHING - A DROSOPHILA MUTATION AFFECTING MEIOTIC CHROMOSOME SEGREGATION IN BOTH FEMALES AND MALES

We describe a Drosophila mutation, Double or nothing (Dub), that cause s meiotic nondisjunction in a conditional, dominant manner. Previously isolated mutations in Drosophila specifically affect meiosis either i n females or males, with the exception of the mei-S332 and ord genes w hich are required for proper sister-chromatid cohesion. Dub is unusual in that it causes aberrant chromosome segregation almost exclusively in meiosis I in both sexes. In Dub mutant females both nonexchange and exchange chromosomes undergo nondisjunction, but the effect of Dub on nonexchange chromosomes is more pronounced. Dub reduces recombination levels slightly. Multiple nondisjoined chromosomes frequently cosegre gate to the same pole. Dub results in nondisjunction of all chromosome s in meiosis I of males, although the levels are lower than in females . When homozygous, Dub is a conditional lethal allele and exhibits phe notypes consistent with cell death.