Inheritance, Variation and Evolution

This unit covers DNA and the genome, meiosis, genetic inheritance and Punnett squares, inherited disorders, sex determination, variation, evolution by natural selection, selective breeding, genetic engineering, speciation and classification.

Genetics needs securing first. Punnett squares are straightforward once the notation is clear, but students lose marks by confusing genotype with phenotype, and by writing ratios where probabilities are asked for. Meiosis and mitosis are examined comparatively, so learn what distinguishes them rather than each in isolation. Natural selection questions reward a structured answer: variation exists, some individuals are better suited, they survive and reproduce, and the advantageous allele becomes more common. Vague answers about animals wanting to adapt earn nothing. Evolution and inheritance connect throughout, so treat the unit as one argument rather than separate topics.