Part b - determining gamete genotypes in trihybrid crosses you have also identified a third recessive mutation that you call crimson. wasps homozygous for crimson have a red abdomen. (wild-type abdomens are yellow.) you make pure-breeding crimson (cc) and triple-mutant (apricot, blunt, crimson) lines. to map the three loci, you perform a trihybrid (three-point) testcross: you first cross crimson wasps with (apricot, blunt) wasps to make an f1, and then you testcross the f1 with the triple-mutant line.