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).

Question

Eugene Cross

Biology

20 December, 20:35

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).

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Kenley Ellis · Answer 1

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