According to Thomas Hunt Morgan, because the genes for body color and wing shape are linked, the predictable F2 offspring phenotypes from a cross between a fly in this cross that is heterozygous for body color and wing shape with another double mutant fly with black body and vestigial wings is 25% wild type phenotype,25% dbl mutant black body/vestigial wings, 25% black body , 25% vestigial wing

75% wild type phenotype and 25% black body/vestigial wing phenotype

100% wild type phenotype

50% wild type phenotype and 50% black body/vestigial wing phenotype