Question

fifty percent of the offspring produced by a cross between pea plants have seeds with a wrinkled (r) appearance caused by the presence of a homozygous recessive gene. what were the genotypes of the parents?

a. rr × rr

b. rr × rr

c. rr × rr

d. rr × rr

Explanation:

To determine the parent genotypes, we analyze each option using Punnett squares:

• Option A (RR × rr): All offspring will be Rr (dominant, round seeds), so 0% wrinkled. Eliminate A.
• Option B (Rr × rr): The Punnett square gives Rr (round) and rr (wrinkled) in a 1:1 ratio, so 50% wrinkled. This matches the problem.
• Option C (RR × Rr): All offspring will be RR or Rr (round seeds), so 0% wrinkled. Eliminate C.
• Option D (Rr × Rr): The Punnett square gives a 3:1 ratio (75% round, 25% wrinkled). Eliminate D.

Answer:

B. Rr × rr