This exam focus covers Exam Focus within Genetic Inheritance for GCSE Biology. Genetic inheritance patterns, alleles, and inheritance diagrams It is section 7 of 9 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 7 of 9
Practice
25 questions
Recall
25 flashcards
Exam Focus
Frequently ExaminedGenetic crosses and Punnett squares are tested in almost every AQA Paper 2. This is one of the highest-mark topics in Unit 7. Common question formats:
- 2-mark Punnett square: Complete a cross, state the ratio, and give the probability. Always show gametes clearly — they are method marks.
- 3-mark explanation: "Explain how two parents with a dominant phenotype can have a child with the recessive phenotype." Requires: heterozygous parents, carrier definition, recessive needs two copies.
- 1-mark probability: Convert Punnett square result to fraction or percentage. Know 1/4 = 25%, 1/2 = 50%, 3/4 = 75%.
- 6-mark extended response: Occasionally tested — describe the mechanism of dominant/recessive inheritance with reference to genotype and phenotype throughout.
Mark-scheme language: When completing a Punnett square, always state the genotype ratios AND the phenotype ratio (e.g., "3 brown : 1 blue", not just "3:1"). Examiners want to see you connect genotype to phenotype.