A horticulturalist wants to produce geraniums with specific characteristics.

Question

She knows that the trait of red flowers is governed by the allele R (RR and Rr) and the trait of white flowers is governed by the allele r(rr).

The horticulturalist crosses two geraniums from the F1 generation.

Look at the Punnett square to see this cross.

R r
R RR Rr
r Rr rr


Which ratio of red-to-white flowering plants would she expect to see in the phenotypes of the F2 generation?

Responses

3 red : 1 white

3 red : 1 white

all red

all red

1 red : 3 white

1 red : 3 white

2 red : 2 white

Answer 1

In the Punnett square you provided, the gametes of the two F1 geraniums (both of which are heterozygous Rr) are crossed. The resulting genotypes from the cross are:

• 1 RR (homozygous red)
• 2 Rr (heterozygous red)
• 1 rr (homozygous white)

To determine the expected phenotypic ratio, we look at the phenotypes of the offspring:

• Red flowers: The genotypes RR and Rr both produce red flowers.
• White flowers: The genotype rr produces white flowers.

Thus, in the F2 generation, there are:

• 3 red flowered plants (1 RR + 2 Rr)
• 1 white flowered plant (1 rr)

This gives us a phenotypic ratio of 3 red : 1 white.

Therefore, the expected ratio of red-to-white flowering plants in the F2 generation is:

3 red : 1 white.