The wild-type eye color in the fruit fly drosophila melanogaster is dark red, as a result of a mixture of bright red and brown pigments. "enzyme a" is encoded by the "a" gene, and is required to synthesize the bright red pigment. a lack of red pigment results in somewhat brown eye color. you cross two fruit flies who are heterozygous for a recessive mutation that completely inactivates the "a" gene. what proportion of their offspring will have a recessive eye color phenotype?