Agene yel- in drosophila is a recessive lethal gene. flies heterozygous (yel+/yel-) have a yellow body color and homozygous flies have brown body color (yel+/yel+). at a second unlinked locus the allele bl for long bristles is incompletely dominant to the allele bs for short bristles. predict the phenotypic ratios for the progeny of the following cross: yellow body, short bristles x yellow body, medium bristles