A heterozygous tall pea plant is allowed to selffertilize Fr

A heterozygous tall pea plant is allowed to self-fertilize. From the F1 progeny, a phenotypically tall plant was randomly chosen and mated to a phenotypically dwarf pea plant. What is the probability of producing any phenotypically dwarf plants from this mating?

Solution

Assume that the gene coding for tall plant is T and the gene coding for dwarf plant is t; T is dominant over t.

Cross between heterozygous plants will have the progeny with the following genotypes:

Tt*Tt -à TT (1/4, tall), Tt (1/2, dwarf), tt (1/4, dwarf)

In order to have a dwarf in the next cross, randomly chosen tall plant must be heterozygous. Thus, the probability of heterozygous tall plant is, 2/3

Cross between heterozygous tall plant and a dwarf plant will have the progeny with the following genotypes:

Tt* tt -à Tt (1/2, tall), tt (1/2, dwarf)

Thus, the probability of producing phenotypically dwarf plants from this mating is = 2/3*1/2 = 1/3.