Can Female Fruit Flies Have White Eyes?
WouterThe gene responsible for eye color is sex-linked. It’s found on the X chromosome and is the only one that female fruit flies can inherit. Females carry the dominant gene W+, while males carry the recessive gene W-. Males have one copy of the gene for eye color on each X chromosome.
Morgan’s study tested this hypothesis by breeding a white mutant fly with a red-eyed female. The F1 offspring he produced all had red eyes. This suggested that a dominant red-eyed gene was influencing eye color. Morgan then bred the F1 offspring with each other and found that the ratio of red-eyed to white-eyed flies was 3:1. Using this method, Morgan discovered that eye color is a sex-specific trait.
Morgan’s study also revealed a link between eye color and chromosomes. He noted that females inherit the white gene allele from both X chromosomes, whereas males only get one copy. Thus, the gene is recessive. This means that a white-eyed female must carry two copies of the white-eye gene on both X chromosomes.
As a genetic model organism, Drosophila simulans is an excellent tool for students to study evolution. Its lab exercise was a great way for students to see the process at work. It also provided an opportunity to see the effects of mutation on gene expression.
