Fig. 3
From: Witnessing Phenotypic and Molecular Evolution in the Fruit Fly
The eye color gene is located on the X chromosome (one of the sex-determining chromosomes of Drosophila). White eye color is recessive. When a red-eyed male mates with white-eyed females, their daughters will have red eyes, but their sons will have white eyes. Therefore, there can be no red-eyed males in the first generation, but they will appear in the second and later generations. From Heil et al. (2013)