Question

When a tall pea plant with round seeds was selfed, it produced the progeny of
(a) Tall plants with round seeds and
(b) Tall plants with wrinkled seeds.
Identify the genotype of the parent plant.

• A. TtRr
• B. TtRR
• C. TTRR
• D. TTRr

Answer 1

Answer: (D)

TTRr

Answer 2

Let’s analyze the given information:
Tall (T) is dominant over dwarf (t).
Round (R) is dominant over wrinkled (r).
The parent plant is tall with round seeds. Since some offspring have wrinkled seeds (rr),the parent plant must carry the recessive allele (r). Because all offspring are tall, the parent plant must carry at least one dominant allele (T).

The offspring phenotypes are:
Tall, Round: Could be TTRR, TTRr, TtRR, or TtRr
Tall, Wrinkled: Must be Ttrr

To produce both round and wrinkled seeds, the parent must be heterozygous for seed shape (Rr). Since all offspring are tall, and wrinkled offspring appear, the parent plant must be homozygous dominant for height (TT). If the parent was heterozygous for height (Tt), then some offspring would have been dwarf (tt), which isn’t observed.
Therefore, the parent’s genotype must be TTRr.