Edexcel GCSE Biology Topic 4 Natural selection and genetic modification: a complete overview of evolution, classification, selective breeding and genetic engineering

What Topic 4 actually demands

Natural selection and genetic modification covers how species change naturally and how humans deliberately change them. The examiners test the four steps of natural selection (often applied to a new example such as antibiotic resistance), the evidence for evolution, the difference between selective breeding and genetic engineering, and balanced "evaluate" answers on GM crops. This guide ties together the four dot-point pages, each with its own practice questions.

Evolution by natural selection

Charles Darwin and Alfred Wallace independently proposed natural selection: there is variation (from mutation), some individuals are better suited to survive, the survivors reproduce and pass on their alleles, and over generations the species changes. Antibiotic-resistant bacteria are strong evidence, because resistant individuals survive the antibiotic and multiply, so resistance spreads, a process fast enough to observe.

Evidence for evolution and classification

The evidence for human evolution comes from fossils (such as Ardi and Lucy), which show brain size increasing and upright walking developing, and from stone tools that become more complex over time. The pentadactyl limb, shared across vertebrates but used for different jobs, points to a common ancestor. Classification moved from five kingdoms to three domains (Archaea, Bacteria, Eukarya) once genetic analysis revealed that prokaryotes are really two groups.

Selective breeding, tissue culture and genetic engineering

Selective breeding chooses and breeds organisms with a desired feature over generations, shaping crops and livestock, but reduces genetic variation. Tissue culture grows many identical plants from a few cells, useful for rare species. Genetic engineering transfers a gene directly: a restriction enzyme cuts the gene, ligase joins it into a vector, and the vector carries it into the host. GM crops bring benefits (yield, pest resistance, nutrients) and risks (gene spread, biodiversity loss), which an "evaluate" answer must weigh.

How Topic 4 is examined

• Applied natural selection. Explaining a new example (resistant bacteria, dark moths) using variation, survival, reproduction and change.
• Evidence questions. What fossils, tools and the pentadactyl limb show.
• Comparisons. Selective breeding versus genetic engineering.
• Evaluate. Balanced judgements on GM crops and agricultural methods.

Check your knowledge

A mix of recall and application questions covering Topic 4. Attempt them under timed conditions, then check against the solutions.

1. State the source of the variation that natural selection acts on. (1 mark)
2. Explain how a population of bacteria becomes resistant to an antibiotic. (4 marks)
3. State one feature, shown by fossils, that changed during human evolution. (1 mark)
4. Explain why the pentadactyl limb is evidence of a common ancestor. (2 marks)
5. Name the three domains of life. (1 mark)
6. Describe the steps a farmer would take to selectively breed cattle for high milk yield. (3 marks)
7. Name the enzyme used to cut a gene out of DNA in genetic engineering. (1 mark)
8. Give one benefit and one risk of growing GM crops. (2 marks)