If a plant variety is true-breeding for a dominant trait, then __________.

• A. if the plant were allowed to self-pollinate, the dominant and recessive traits would consistently appear in a 3:1 ratio among the progeny
• B. the plant is heterozygous for the trait
• C. if the plant were crossed with a heterozygote, one-half of the progeny would show the dominant trait, and one-half would show the recessive trait
• D. the variety is unable to mutate
• E. if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait

Answer: (E)

Verified step by step guidance

1. Understand the concept of true-breeding: A true-breeding plant is one that, when self-pollinated, produces offspring that are genetically identical to the parent for a specific trait. This means the plant is homozygous for the trait.
2. Identify the nature of the trait: Since the plant is true-breeding for a dominant trait, it must be homozygous dominant. This means its genotype is represented as $\mathrm{AA}$, where 'A' is the dominant allele.
3. Consider the self-pollination process: When a homozygous dominant plant self-pollinates, it can only pass on the dominant allele to its progeny. Therefore, all offspring will inherit the dominant allele from both parents, resulting in a genotype of $\mathrm{AA}$.
4. Analyze the progeny traits: Since all progeny have the genotype $\mathrm{AA}$, they will all express the dominant trait phenotypically.
5. Conclude the outcome: Therefore, if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait, confirming the correct answer.