(Problem 20a and b) Waxy endosperm (wx), shrunken endosperm (sh), and yellow see
ID: 93949 • Letter: #
Question
(Problem 20a and b) 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 10,756Explanation / Answer
Here Answer is D
Wx-sh-V (3479) & wx-sh-v (3478) are parental progeny, due to its high number
wx-sh-V (87) & Wx-Sh-v (94) are Double cross overs due to its minimum number
By comparing, Parental progeny with Double cross overs, we can deside middle gene. Here the middle gene is "V"
So the gene order is either Wx-----V------Sh or Sh----V------Wx
wx----Sh----V & Wx---sh---v are single cross overs between Wx & V. Then Distance between Wx & V =
Total number of Single cross overs between Wx & V + Double cross overs x 100 / Total progeny
= (292+ 280+ 87 + 94) x 100 / 10,756
= 7% = 7 m.u
If we do the same, for single cross overs between Sh & V
= (1515+1531+87+94) x 100 / 10,756
= 30 % = 30 m. u
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