Interallelic complementation of modifier msl1 mutations. (a) The percentage male viability is shown for each allelic combination. The msl1 allele donated by one parent is on the Y axis and the allele donated by the other parent is on the X axis. The Df allele is msl1L60. The number in parentheses is the number of msl1a/msl1b daughters recovered in each cross. The thicker bars indicate the modifier alleles recovered in the mosaic eye screen. The P864L/S943F heterozygotes used in the longevity assay are boxed. The rare msl1/Df male escapers eclosed late, had held out wings, and pale mosaic eyes. (b) The viability for all combinations of S943F males are shown with the second allele indicated by the right axis. (c) The longevity of the four classes of progeny recovered from a cross between msl1P864L/CyO and msl1S943F/CyO parents. Although msl1P864L/msl1S943F males and females were initially recovered in nearly equal numbers, the adult males appeared weaker, held out their wings, and had shorter lifespans. The starting populations were > 150 adults per genotypic class.