Question

Through mutagenesis you have isolated 2 drosophila mutants that both have an extra set of legs bodies (d and l). After isolating a purebreeding specimens of each mutation. What would be the complementation test to determine if they are the same gene or not assuming they are both recessive? (a) d/d (b) D/d (c) D/d x l/l (d) D/D x x L/l (e) d/d x l/l L/L x L/L

Answer 1

Ans: e) d/d x l/l L/L x L/L OR ddLL x DDll

Drosophila mutants have the mutant alleles d and l. Presence of either of these alleles in homozygous recessive condition (dd or ll) produce extra legs. The alleles D and L are working complementary with each other to produce normal number of legs. But here, the mutation produced extra legs.

Complementation test is done with ddLL with DDll. If both the alleles D and L are present in dominant form, then the particular phenotype, extra legs will not be produced since it is a mutated character. Thus the heterozygous DdLl can not produce the extra legs. Mutation in any one gene (d or l) will produce the phenotype, extra legs.

The issue is whether they (alleles) are on the same gene or on different genes. If they are on the same gene, complementation will not happen. If they are on different genes, complementation will happen. For this the complementation test is done with one organism having one recessive allele (dd) and dominant allele (LL) WITH the other organism having one dominant (DD) and one recessive (ll) allele.