You are studying wing size in the fruit fly Drosophila melan

You are studying wing size in the fruit fly Drosophila melanogaster. You have four pure-breeding lines of flies (named small1.small2, etc) with abnormally small wings. You have already determined that in each of the lines, small wings are recessive to wild-type wings. You now perfom complementation testing on the four lines. Results of crosses between the lines are given in the table below. indicates the progeny have wild-type-size wings, and indicates small wings How many independent genes are represented here? List the alleles corresponding to each of the independent games Why is it important to determine whether a mutation is dominant or recessive before performing a complementation test?

Solution

5. b) The complementation test must be performed with recessive mutations only. Dominant mutations are not useful for complementation tests because dominant alleles cause mutant phenotypes even if the other allele of the gene is wild type. Hence, domiannt mutations can be recognised in complementation tests by their failure to complement any other mutation. So, it is important to determine whether a mutation is dominant or recessive before performing a complementation test.