Question

You are working with the fruit fly that generally exhibits a brick red eye color (wild-type). In one stock vial you recover an eye color mutant with brown eyes that you use to eventually derive a pure-breeding brown-eyed stock. Your friend, performing independent studies on the fruit fly, also recovers a pure breeding brown eye color mutant that is phenotypically identical to your strain. How would you go about determining if the two pure-breeding brown-eyed mutant strains represent mutations in a single eye color gene or in two different eye color genes? Explain how you would distinguish between the two different genetic models.

Answer 1

Complementation test needs to be performed with the two pure breeding mutant brown eyed fly strains. These two mutant strains are phenotypically identical and can therefore have mutations in the same eye color gene or different genes. The two strains should be crossed and the progeny observed for eye color phenotype. If the progeny has brown colored eyes as that of the parents, then no complementation has occured and the parental mutations were in the same gene. But if the progeny shows wild type brick red eyes, then complementation of gene products has occurred (different deficient gene product coming together to complete the pathway) and the parental mutations were in different eye color genes.