(Problem 20c) Waxy endosperm (wx), shrunken endosperm (sh), and yellow seedling

Question

(Problem 20c) Waxy endosperm (wx), shrunken endosperm (sh), and yellow seedling (v) are encoded by three recessive genes in corn that are linked on chromosome 5. A corn plant homozygous for all three recessive alleles is crossed with a plant homozygous for all the dominant alleles. The resulting F1 are then crossed with a plant homozygous for the recessive alleles in a three-point testcross. The progeny of the testcross are as follows:

wx sh V 87 Wx Sh v 94 Wx Sh V 3,479 wx sh v 3,478 Wx sh V 1,515 wx Sh v 1,531 wx Sh V 292 Wx sh v 280 Total 10,756

Explanation / Answer

As per previous submission, the map distance between Wx & V is 7 mu and Sh & V is 30 mu.

Coefficient of coincidence = No. of observed double cross overs / No. of Expected double cross overs

Expected double cross overs frequency = product of single cross over frequencies (map distance / 100 = frequency)

= 0.07 x 0.3 = 0.021

Number of expected double cross overs = 0.021 x Total progeny = 0.021 x 10,756 = 225.8

So Coefficient of coincidence = (87+94) / 225.8

= 0.8

Then Interference - 1- Coefficient of coincidence = 1-0.8 = 0.2

So answer is A

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