Explain how a gene controls a characteristic in an organism, using plant height as an example. Your answer should connect genes, enzymes, hormones and the final trait.
Generated by claude-sonnet-4-6 · 2026-06-26 01:03 · grounding rag
Model Answer
A gene is a segment of DNA that controls a specific characteristic by directing the synthesis of a particular enzyme.
For example, in pea plants, the gene for height (T/t) controls the production of enzymes that regulate the synthesis of plant hormones (such as gibberellins). These hormones promote cell elongation.
- The dominant gene T directs enzyme production that leads to higher hormone levels → tall plant.
- The recessive gene tt results in reduced enzyme activity → lower hormone levels → short plant.
Thus, the gene → enzyme → hormone → final trait (height) pathway determines the characteristic expressed.
Source: Chapter 8, Section 8.2.2; Chapter 6, Section 6.2
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Explanation
- The examiner expects you to link the four terms in a logical chain: gene → enzyme → hormone → trait. Missing any link loses marks.
- The T/t example from Mendel (Chapter 8) is the prescribed context; gibberellin is the relevant plant hormone for height (Chapter 6 mentions plant hormones).
- Note: the source passages do not explicitly detail the enzyme-hormone chain for height, so use your textbook knowledge to bridge gene → enzyme → hormone, but keep the Mendelian T/t example as your anchor.
- Dominant (TT/Tt = tall) and recessive (tt = short) language from the passage should appear to show you understand the gene-to-trait connection.