In Drosophila, Mutation Screening Usually Involves Use of a Balancer

Multiple Choice

In Drosophila, mutation screening usually involves use of a balancer chromosome that includes three elements: a set of overlapping inversions, an easily recognized dominant mutation, and a recessive lethal mutation that prevents balancer homozygotes from surviving. Which one, or combination, of these elements is necessary and sufficient to suppress crossovers?

A) inversions
B) dominants
C) lethal recessive
D) inversions plus dominant
E) lethal plus inversions