In a plant, shortness is controlled by a gene that produces a less efficient enzyme, resulting in lower hormo…

Question

In a plant, shortness is controlled by a gene that produces a less efficient enzyme, resulting in lower hormone levels. Tallness is controlled by an efficient form of the same enzyme. Which form of the gene is dominant?

Accepted Answer

## Model Answer **Answer: (B)** The gene producing the efficient enzyme is dominant, because even a single copy produces enough hormone to make the plant tall, while two copies of the less efficient gene are needed for shortness. *Source: Heredity, Section 8.2.2* --- ## Explanation The textbook states: *"a single copy of 'T' is enough to make the plant tall… traits like 'T' are called dominant traits."* Dominance means one copy is sufficient to express the trait. Here, one copy of the efficient-enzyme gene produces enough hormone for tallness — exactly the definition of a dominant allele. The less efficient enzyme gene requires two copies (homozygous recessive) to show shortness, making it recessive.

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