3(b) Inheritance
Pearson Edexcel International GCSE Biology · 4BI1
Paper 2 | Whole paper: All content including bold B statements
DNA, genes, chromosomes, and how to predict the outcome of a cross with a genetic diagram.
Specification coverage
Topic 3 Reproduction and inheritance (b) Inheritance — statements 3.16–3.32B (includes bold B statements assessed on Paper 2 only)
Assessment objectives: AO1, AO2. Suggested learning time: 120 minutes.
Required knowledge
- The structure of DNA, chromosomes and genes, and the meaning of genotype, phenotype, allele, dominant, recessive, homozygous and heterozygous
- Mitosis and meiosis, and the role of each
- Monohybrid inheritance and the use of Punnett squares and genetic diagrams
- Sex determination in humans
- Codominance and sex linkage
- Mutation as a change in a gene or chromosome, and the effect of ionising radiation on mutation rate
- Variation: genetic, environmental, continuous and discontinuous
- Natural selection and evolution, and the development of resistance
- Bold B statements: further genetic crosses and probability in greater depth
Required skills
- Construct a complete genetic diagram: parental phenotypes, genotypes, gametes, offspring genotypes, offspring phenotypes and ratio
- Predict the probability of an outcome from a cross
- Explain resistance as an example of natural selection
How it is examined
- Multiple-choice and short-answer recall
- Application of the content to an unfamiliar context
- Extended open-response, marked on the quality of a connected explanation
Common mistakes
- Skipping steps in a genetic diagram. Each labelled row carries a mark, so a correct answer with no working scores badly.
- Confusing mitosis and meiosis. Meiosis halves the chromosome number and produces genetically different gametes.
- Saying an organism 'develops' resistance during its lifetime. Resistant individuals already existed; selection increased their frequency.