In drosophila, red eyes is the wild-type phenotype. Several different genes (with each gene existing in two or more alleles) are known to affect eye color. One allele causes purple eyes, and a different allele causes sepia eyes. Both of these alleles are recessive to red eye color. When flies with purple eyes were crossed to flies with sepia eyes, all the F_1 offspring had red eyes. When the F_1 offspring were allowed to mate with each other, the following data were obtained: 146 purple eyes
151 sepia eyes
50 purplish sepia eyes
444 red eyes
Explain the pattern of inheritance.