Question

The production of eye color pigment in Drosophila requires the dominant allele A. The dominant allele P of a second independent gene turns the pigment to purple but its recessive allele leaves it red. A fly producing no pigment has white eyes. Two pure lines were crossed with the following resultsP: red-eyed female X white-eyed male

F1: purple-eyed females and red-eyed males
F2 (from F1 X F1): both males and females 3/8 purple-eyed, 3/8 red-eyed and 2/8 white-eyed
Explain this mode of inheritance and show the genotypes of the parents, the F1 and the F2.

Answer 1

Eye color in Drosophila is determined by the X-linked dominant alleles A for pigment production and P for purple color. A cross between a red-eyed female and a white-eyed male results in F1 purple-eyed females and red-eyed males, followed by a 3:3:2 ratio of purple: red: white-eyed F2 offspring.

Step-by-step explanation:

The eye color inheritance in Drosophila is an example of an X-linked cross where the phenotype depends on the genotypes of the parents. Here, the dominant allele A is necessary for eye color pigment production, and the dominant allele P turns the pigment to purple, while its recessive form leaves it red. If no pigment is produced, the eyes are white. The pure red-eyed female is homozygous (XWXWAPAP) and the white-eyed male is hemizygous for white and also lacks the A allele (XYAy). The F1 generation consists of purple-eyed females (XWXYAPAy) and red-eyed males (XYAP). For F2 (XWXYAPAy crossed with XWXYAPAy), we see a 3:3:2 ratio of purple: red: white-eyed offspring, which means the eye color and pigment production genes are segregating independently.