This exam focus covers Exam Focus within Sex Determination for GCSE Biology. Sex chromosomes and sex determination mechanisms It is section 9 of 11 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 9 of 11
Practice
26 questions
Recall
20 flashcards
Exam Focus
Regularly ExaminedSex determination is tested regularly in AQA Paper 2. Common question formats:
- Genetic diagram: Draw the Punnett square for sex determination, identify gametes, state the probability as a ratio and percentage.
- Explain questions: "Explain why the father determines the sex of the child." Answer must include: mother always gives X, father gives X or Y, Y = male, X = female.
- Higher tier — X-linked disorders: Given a pedigree diagram, identify carriers and affected individuals. Calculate probability of an X-linked condition in sons.
- Common error question: "A couple say the mother determines the baby's sex. Evaluate this claim." Requires a clear correction with genetic explanation.
Mark-scheme tip: When completing a sex determination genetic diagram, always write the gametes explicitly (X and Y for father; both X for mother) before filling in the Punnett square — these carry method marks.