Specification references covered: µþ3.14–B3.16 (Punnett squares; family pedigree charts; sex determination; probabilities, ratios and percentages from monohybrid crosses)

Inheritance brings together all the genetics vocabulary from CB3c and applies it to calculation questions, pedigree reading, and sex determination diagrams.

The Topic Mastery Sheet provides a six-step Punnett square method with a fully worked cystic fibrosis example from the official mark scheme, a guide to reading pedigree symbols and deducing genotypes, a worked percentage calculation with the examiner note about the % sign, and a complete sex determination diagram.

The Student Exam Practice Sheet (20 marks) includes: Huntington’s probability MCQ, Ff×Ff Punnett square, probability calculation, genotype identification, genetic disease definition, pedigree deduction, RP percentage calculation, sex determination diagram, achondroplasia cross explanation, and a Higher Tier genotype uncertainty question.

The Teacher Answer Key flags the probability vs ratio distinction explicitly (1:3 is rejected; 25%/¼/0.25 are all accepted) and gives the sex determination mark scheme exactly as worded in the official paper.

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