Now we'll do a second cross.Note that the key is to set up a parent that is heterozygous at two loci. sh+ (cinnabar eyes) cn ♀动+ sh cn +cn sh cn sh cn 12 sh ch crossover classes 8 sh cn cn 493 sh cn sh 487 sh cn Distance between sh and cn=2 cM 一8cM一 12 cM- shcn vg cn sh vg -10cM- —10cM- There are two possible orders.We could resolve them by measuring the cn to vg distance,which should be either 8 cM or 12 cM depending on the order.However,it's difficult in practice to get a statistically significant measurement that would cleanly distinguish between these possibilities. A better way to find the order is to set up all three heterozygous markers at the same time and to look at the frequencies of the eight different gamete genotypes.Now we’ll do a second cross. Note that the key is to set up a parent that is heterozygous at two loci. O sh + +cn x O (cinnabar eyes) sh + + cn ↓ sh + sh cn O x O +cn shcn ↓ sh cn 12 sh cn crossover classes + + 8 sh cn +cn 493 sh cn sh + 487 sh cn Distance between sh and cn = 2 cM There are two possible orders. We could resolve them by measuring the cn to vg distance, which should be either 8 cM or 12 cM depending on the order. However, it’s difficult in practice to get a statistically significant measurement that would cleanly distinguish between these possibilities. A better way to find the order is to set up all three heterozygous markers at the same time and to look at the frequencies of the eight different gamete genotypes