wo different true-breeding lines of the Carolina Blue Bottle fly (genetics identical to Drosophila) are crossed and F1 females from this cross are then crossed to males from a line that is homozygous for four different recessive traits. A total of 1000 progeny from these crosses are then evaluated for each of the four traits. For simplicity, the recessive traits are designated a, b, c, and d while the corresponding dominant traits are designated with a "+". The phenotypes and number of each of the sixteen possible phenotypic classes are given below: