Q1. [3] deep thorough-understanding
In a class, some students have free earlobes and some have attached earlobes. A student notices that both her parents have attached earlobes, yet she has free earlobes. What does this tell us about the inheritance of earlobe type, and what does it reveal about the nature of the free earlobe trait? Justify your answer.
Generated by claude-sonnet-4-6 · 2026-06-26 01:03 · grounding rag
Model Answer
Both parents have attached earlobes, yet the student has free earlobes. This tells us that earlobe type is inherited — it follows Mendel's rules of inheritance, where each child receives genetic material from both parents.
Since both parents have attached earlobes but still produced a child with free earlobes, the free earlobe trait must be recessive. The parents each carried one copy of the free earlobe gene (recessive) without expressing it, as attached earlobe is the dominant trait. When the child inherited one recessive copy from each parent, she expressed the free earlobe trait.
Source: Chapter 8, Section 8.2.2 — Rules for the Inheritance of Traits
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Explanation
- The key logic: if a trait "skips" a generation (parents don't show it but child does), the trait is recessive.
- Parents with attached earlobes must be heterozygous (Aa) — carrying one dominant (A) and one recessive (a) allele. The student received aa, expressing the recessive free earlobe.
- Examiners expect you to use the terms dominant and recessive correctly and justify with Mendelian reasoning. Avoid vague answers like "it skipped generations" without explaining why.