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Chromosome mapping and coefficient of coincidence

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The F1 Lobe females were then backcrossed with homozygous smooth abdomen, straw body males and the following phenotypes were observed:

smooth abdomen, straw body 820
Lobe 780
smooth abdomen, Lobe 42
straw body 58
smooth abdomen 148
Lobe, straw body 152

(a) Give the gene order and map units between these three loci - draw the map!.
(b) What is the coefficient of coincidence?

Solution Summary

Chromosome mapping can be done on the basis of F1 testcross results. Coefficient of coincidence is the ration of the observed to the expected frequency of the double cross-over.