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Chromosome mapping and coefficient of coincidence

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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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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.

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Chromosome mapping and coefficient of coincidence.

In the fruit fly, Drosophila melanogaster, a spineless (no wing bristles) female fly is mated to a male that is claret (dark eyes) and hairless (no thoracic bristles). Phenotypically wild type F1 female progeny were mated to fully homozygous (mutant) males and the following progeny (1000 total) were observed.

PHENOTYPES NUMBER OBSERVED

spineless 321
wild 38
claret, spineless 130
claret 18
claret, hairless 309
hairless, claret, spineless 32
hairless 140
hairless, spineless 12

(a) What are the map distances between the three genes? Draw the map.
(b) What is the coefficient of coincidence?

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