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

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

a. Determine the order of these genes on the chromosome.
b. Calculate the map distance between the genes.

(a) See the answer in the explanation below

(b) Distance between wx and v = 7 mu

    Distance between gene v and sh= 30 m.u.

Explanation:

(a) The order of the genes are given below;

wx          sh               V               87 (double crossover)

Wx         Sh               v                95 (double crossover)

Wx         Sh              V                3479 (NCO/parental)

wx         sh               v                 3478 (NCO/parental)

Wx        sh               V                1515 (Single crossover between v and sh)

wx        Sh               v                1531 (Single crossover between v and sh)

wx       Sh               V                292 (Single crossover between wx and v)

Wx       sh               v                280 (Single crossover between wx and v)

Total                                          10,756

(b) To calculate the distance between genes, we use the formula;

Recombination frequency = number of recombinant progeny/total number of progeny *100

 Distance between V and Sh = 1515+1531+87+94/10756 *100

                                                = 3227/10756 *100

                                                = 30% or 30 mu

Therefore, distance between V and Sh = 30 mu

Distance between wx and v = 292+280+87+94/10756 *100

                                              = 753/10756 *100

                                              = 7% or 7 mu

Therefore, distance between wx and v = 7 mu

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explanation: