Q1. [1] medium thorough-understanding
[mcq] A pea plant has the genotype Tt. Which of the following best explains why it appears tall?
(A) Both T and t alleles combine to produce an intermediate height that is still classified as tall.
(B) The T allele is dominant and its single copy is sufficient to express the tall trait, masking the effect of t.
(C) The t allele mutates into T during plant development, giving a full tall phenotype.
(D) The plant expresses tallness because T alleles are always more numerous than t alleles in body cells.
- A It has two copies of the T allele, both contributing to tallness.
- B One copy of T is sufficient to produce enough hormone to make the plant tall, so the t allele has no visible effect.
- C The t allele is lost during cell division, leaving only T to be expressed.
- D The T and t alleles blend to produce a medium height, which is classified as tall.
Generated by claude-sonnet-4-6 · 2026-06-26 01:03 · grounding rag
Model Answer
(B) The T allele is dominant and its single copy is sufficient to express the tall trait, masking the effect of t.
Explanation
The textbook states clearly: "a single copy of 'T' is enough to make the plant tall." Both TT and Tt are tall; only tt is short. Examiners expect students to use the terms dominant and recessive and the idea that one copy of a dominant allele is sufficient for expression.