In Drosophila, the genes b, c, and sp are linked and in the order given, the distances being b-c = 30 m. u. and c-sp = 20 m. u. These intervals exhibit 90% interference. How many double crossovers would be recovered in a three-point cross involving b, c, and sp out of 1000 progeny?

Explanation:

Double cross over or three point test cross is helpful:

Interference is the physical phenomenon in which crossing over of a gene suppresses its neighbouring gene to cross over due to the physical property of genes

In the given question:

Distance between b-c = 30 m.u.

Distance between c-sp = 20 m.u.

Interference(I) = 90%=90/100=0.9

Progeny = 1000

DCO stands for double cross over  

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