Two true-breeding stocks of pea plants are crossed. One parent has red, axial flowers and the other has white, terminal flowers; all F 1 individuals have red, axial flowers. If 1,000 F 2 offspring resulted from the cross, approximately how many of them would you expect to have red, terminal flowers? (Assume independent assortment).

187.5 or rounded off to 188 white, terminal flowers

Explanation:

Let red=R and white=r where R>r; axial=A and terminal=a where A>a

The parents are true-breeding which means that they are homozygous.

P: RRAA x rraa

F1: RrAa

We then cross two plants from the F1 generation

RrAa x RrAa

To find out the probability we look at the different traits individually

Rr x Rr

yielding 1/4 RR (red), 1/2 Rr (red), 1/4 rr (white)

Aa x Aa

yielding 1/4 AA (axial), 1/2 Aa (axial), 1/4 aa (terminal).

We determine which F2 genotypes would allow for red, terminal flowers.

RRaa and Rraa

Then we use the multiplication rule to determine the probability of these occurring

RRaa: 1/4 x 1/4 = 1/16

Rraa: 1/2 x 1/4 = 1/8

Next we use the addition rule

1/16 + 1/8 = 3/16

To find out the number of these plants within the 1000 F2 plants we multiply the probability with 1000

3/16 x 1000 = 187.5 red, terminal flowers