Waxy endosperm (wax), shrunken endosperm (sh), and yellow seedling (v) are encod
ID: 94690 • Letter: W
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 belowExplanation / 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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