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

The Correct Option is D

To solve the question of identifying the genotype of the parent pea plant, we need to understand Mendelian genetics and the concept of dihybrid crosses. The parent plant in question is a tall pea plant with round seeds that produced progeny with both round and wrinkled seed phenotypes. Here's how we identify the correct genotype:

1. Phenotypic Analysis: The parent plant is described as tall with round seeds.
   • Tallness (T): Tallness is dominant over dwarfness. So for the tall phenotype, the genotype could be TT or Tt.
   • Seed Shape (R): Round seeds are dominant over wrinkled seeds. Therefore, the genotype could be RR or Rr.
2. Progeny Analysis: The progeny consists of tall plants with round seeds and tall plants with wrinkled seeds.
   • The appearance of progeny with wrinkled seeds (recessive trait) indicates that the round seed parent must have contributed an r allele, confirming a heterozygous condition, Rr.
   • Since all the progeny are tall, the phenotype is consistently dominant for tallness, which does not rule out either homozygous TT or heterozygous Tt.
3. Conclusion: Based on the progeny analysis, the genotype must include a heterozygous condition for seed shape (Rr), leading to two options for the genotype: TTRr or TtRr.
   • However, the question provides options where TTRr is available, providing the dominant phenotype for height and the required heterozygous condition for seed shape. Thus, the correct genotype for the parent plant is TTRr.

The correct answer is TTRr.