Exam Focus

Exam Focus

Inherited disorders are a core topic on AQA Paper 2 and Edexcel 1BI0/1 (Paper 1). Common question formats:

• Punnett square with probability: Carrier x carrier cross (Ff x Ff), state probability of affected child as fraction and percentage.
• Explain questions: "Explain why a child can have CF even though both parents are healthy." Requires: carrier definition, recessive allele needs two copies, Punnett square evidence.
• Compare CF and polydactyly: Be clear that CF is recessive (both parents must be carriers) and polydactyly is dominant (one affected parent is enough).
• Evaluate genetic screening: 4-6 mark questions ask you to weigh benefits vs ethical concerns. Include both scientific (disease prevention) and ethical (autonomy, discrimination) arguments.

Edexcel 1BI0 style: Edexcel Paper 1 (1BI0/1) often uses real case studies or news article extracts as stimulus for inherited disorder questions — for example, a passage about a family affected by cystic fibrosis or a description of prenatal genetic testing. You are expected to apply your genetic knowledge to the specific scenario. The command word "Suggest" may ask you to reason about an unfamiliar inherited condition using the same principles you know for CF and polydactyly. Edexcel mark schemes use "Allow recessive gene" as well as "recessive allele" — both phrasings are credited.

Key distinction to memorise: CF = recessive (ff), polydactyly = dominant (P). This is almost always tested as a "state which type is recessive/dominant" question.