What is the 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?

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