Question

1. S. superis is a rare flowering plant that can produce blooms in two colours, purple (P) and teal (p), and two shapes, four petals (F) and seven petals (f). Purple is dominant to teal, and four is dominant to seven petals. S. superis is a diploid organism, 2n = 4, that can both self-fertilize and mate with other plants of the same species (out-cross).

You find one of these rare plants in your garden and it has purple flowers with four petals. Assuming this lonely plant must self-fertilize what potential offspring phenotypes could you see?

Select one:

a. Purple with seven petals

b. Purple with four petals

c. Teal with seven petals

d. All of the phenotypes listed are possible depending on the genotype of the plant.

Part B:

Your friend is working with S. superis plants in the lab and has set up a cross between a plant with four purple petals and a plant with seven teal petals. Of the 200 offspring from the cross all have purple petals but about 1/2 have four petals and 1/2 have seven petals. If you were to write out the cross that your friend set up what would it look like genotypically?

Select one:

a. PPFF X ppff

b. PpFf X ppff

c. PpFF X ppff

d. PPFf X ppff

e. PpFf X PpFf

Answer 1

1. Ans is (d) All of the phenotype listed are possible depending on the genotype of the plant.

Let me proove it:

(A)Suppose the genotype is P_Ff, then (a) is fulfilled that is purple with seven petals(P_ff)

(B)If the genotype is P_F_ then all the phenotypes are possible and (b) is fulfilled.

(C) if the genotype is PpFf l, then point (c) real with seven petals (ppff) is fulfilled.

Part B: Ans is (d) PPFf * ppff

Reason: This is an example of dihybrid test cross. In this kind of test cross we have to determine an unknown genotyoes of 2 genes showing dominant phenotype by crossing it with its recessive counterpart. In these kind of questions we have to focus on one trait at a time. If on Testcrossing all offsprings show dominant phenotype then the unknown genotype is homozygous dominant. If on Testcrossing half of the offsprings show dominant phenotype and half of the offsprings show recessive phenotype then the unknown genotype is heterozygous dominant.

In this question, on Testcrossing plant having purple flowers with four petals(P_F_ : dominant phenotype but unknown genotype) with plant having seven petals real flower (ppff - recessive counterpart) :

All of the offsprings have purple flowers that means purple phenotype is homozygous dominant(PP)

Half of the offsprings have four petals and other half have seven petals that means four oetal phenotype is heterozygous dominant (Ff)

Hence genotype of plant with purple flowe with four petals is PPFf.