| Balancer chromosomes present in the mutagenized population and in the wild-type mates to which they are crossed prevent recombination and thus prevent the separation of the new mutation (m) from the dominant marker (in this case Pm, which gives purple eyes) on the same chromosome. The balancer chromosome also carries a dominant marker (Cy in this case, which gives "curly wings") and so flies carrying both the mutagenized chromosome and the balancer chromosome can be detected directly in the F1 generation and selected for further breeding. The Cy mutation is lethal when homozygous, so that organisms that inherit two balancer chromosomes die as embryos. |
