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# How to calculate distance between gene on a chromosome

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Assume that the genes for tan body and bare wings are 15 map units apart on chromosome II in Drosophila. Assume also that a tan-bodied, bare-winged female was mated to a wild type male and the resulting F1 phenotypically wild type females were mated to tan-bodied, bare- winged males. Of 1000 offspring, what would be the expected phenotypes and in what numbers would they be expected?

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#### Solution Summary

Number of recombinants is directly proportional to the distance between genes in map unit. This relationship is utilize in calculating the number of phenotypes.

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## Determine the linear sequence of these three genes

In Drosophila, a cross was made between females expressing the three X-linked recessive traits: scute (sc) bristles, sable (s) body and vermillion (v) eyes, and wild-type (+) males. In the F1, all females were wild-type, while all males expressed all three recessive traits. The cross was carried to the F2 generation and 1000 offspring were counted with the results shown below.
Offspring #
sc s v 314
+ + + 280
+ s v 150
sc + + 156
sc + v 46
+ s + 30
sc s + 10
+ + v 14

Determine the linear sequence of these three genes.
What is the map distance between these genes?
Is there evidence of interference? If so, calculate it.

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