Waxy endosperm (wax), shrunken endosperm (sh), and yellow seedling (v) are encod

Question

Waxy endosperm (wax), shrunken endosperm (sh), and yellow seedling (v) are encoded by three recessive genes in con 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 F are then crossed with a plant homozygous for the recessive alleles in a three-point testcross. The progeny of the testcross are below and listed in a random order. 87 94 3,479 3,478 1,515 1,531 Wx Sh Sh 292 Sh280 sh Total 10,756 Place each gene in the correct order on the chromosome below locus 1 locus 2 locus 3 wX Continued below

Explanation / Answer

The solution of the following Question:

The nonrecombinants are Wx Sh V and wx sh v.The double crossovers are wx sh V and Wx Sh v.Comparing the two, we see that they differ only at the v locus, so v must be the middle gene

Wx–Vdistance—recombinants arewx VandWx v:RF= (292 + 280 + 87 + 94)/10,756 = 753/10,756 = 0.07 = 7%, or 7 m.u.

Sh–Vdistance—recombinants aresh VandSh v:RF= (1515 + 1531 + 87 + 94)/10,756 = 3227/10,756 = 30 = 30% or 30 m

Coefficient of coincidence

Expected double crossovers =RF1 ×RF2 × total progeny = 0.07(0.30)(10,756)= 226

coefficient of coincidence = observed double crossovers/expected doublecrossovers = (87 + 94)/226 = 0.80

interference among these genes

Interference = 1 – coefficient of coincidence = 0.20

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