Learning objective

Use direct proportion and simple ratios in sex-determination genetic crosses.

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At a glance

Flashcards

Questions

Topic

Reproduction

Subtopic

Sex determination

AQA GCSE BiologyInheritance, variation and evolution

Study support

Understand this objective

Short explanation

Use direct proportion and simple ratios in sex-determination genetic crosses.. Within Reproduction, this learning objective sits inside Sex determination for AQA Biology 8461. Focus on using ideas such as direct proportion, genetic cross, ratios accurately in your explanation. A strong response should define the core idea, describe the relevant biological process, and connect it back to the question wording instead of giving a vague definition. When revising, students should aim to explain the science clearly, include precise biological vocabulary, and show how the process or structure links to the wider topic rather than listing isolated facts.

Key concepts

Genetic crossDirect proportion

Why it matters

This objective helps connect Sex determination to exam-style questions, flashcards, and revision notes for Reproduction.

Common mistakes

1 linked

Misinterpreting Ratios in Sex‑Determination Crosses: Explain that the 1:1 ratio applies only when one parent contributes a single sex chromosome (XX or XY) and the other contributes a single sex chromosome (XY). Use a simple Punnett square to show how the ratio changes when both parents are XY (giving 1/4 XX, 1/2 XY, 1/4 YY) or when both are XX (all XX). Emphasise that the ratio is derived from the proportion of gametes, not a universal rule.

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