Identifying recessive mutations in Drosophila using a balancer chromosome

Balancer _______cn+++ d Cn+++ ‘ chromosome £ 0 Mutagenize sperm cells. p 9 m x a Mate with a female fly carrying a balancer C . bal -. chromosome. IS a ancer , . . cl‘rgmosome The cmnabar mutatIon (cn) IS with a dominant included to help follow the balancer allele resulting \ and mutagenized chromosomes. in curly wings and a recessive 9 Select male F progen y , lethal allele. with curly wings, carrying ‘ the CyO mutation, and F1 6' a ‘23; x 9 722+; mate with a female fly carrying the balancer chromosome. 0 Select F progeny ++++ with curly wings and F2 cinnabar eyes, cn+m+ carrying dominant CyO and homozy- gous for the recessive chyO cn allele. (These have inherited the original mutagenized d1romosome and a balancer chromo- some.) QInterbreed within aselected F2. Homozygous? amid l . for m mutation / chyO Heterozygous form mutation chyO ( . If no straight-winged flies are present in F3 progeny, the new mutation is lethal.