1. In garden peas, an allele T for axial flowers (positioned along the stem) is

Question

1. In garden peas, an allele T for axial flowers (positioned along the stem) is dominant to an allele t for terminal flowers (positioned at the tips of the branches).

a) Use a Punnett square to predict the expected ratio of axial: terminal flowers in the F2 generation of a monohybrid cross between these two parental types. Please include Punnett square in your answer.

b) Among the F2 progeny, what proportion is heterozygous?

c) Among the F2 progeny with axial flowers, what proportion is heterozygous?

d) In a testcross of the F1 progeny of a monohybrid cross, what is the expected ratio of axial: terminal?

Explanation / Answer

Punnet square

           T                t

T       TT               Tt

t         Tt                tt

Axial flowers are 3 ( TT , Tt , Tt)

Terminal flower 1 (tt)

Ratio = 3 : 1

(b) 50% are heterozygous (Tt)

(c) Heterozygous have axial flowers because T is dominant to t . So propotion of axial flowers = 50%

(d) Test cross of F1 progeny means Tt x Tt which has been already done in the first example.

Ratio of axial : terminal = 3 : 1

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