Cross between a white-eyed female and a white-eyed male drosophila?

Answer 1

For fruit flies, having white eyes is a recessive trait. It is also a sex-discriminant trait because its gene is located on the X sex chromosome. So knowing this, let's decide what the genotypes of the flies are.

Your white-eyed female is expressing a recessive trait and because it is female, it has two X sex chromosomes. The gene for eye color is on both of these chromosomes. If the fly had the gene for red eyes on either or both of these chromosomes, it would be the dominant trait and would cause the fly to have red eyes, but it doesn't. So we deduce that the female's genotype is ww or two recessive genes.

Your white-eyed male is expressing a recessive trait and has one X chromosome and one Y chromosome. Because only X chromosomes contain the gene for eye color, we can ignore the Y chromosome in this situation. We deduce that the male fly's genotype is wY for eye color, or one recessive gene and a Y chromosome that is indicated for gender.

The next generation will not have any w+ or wild type red eye color at all. 50% of your next generation's flies will be white eyed males and 50% of your next generation's flies will be white eyed females.