Edexcel GCSE Biology
Variation, evolution and selection — Edexcel GCSE Biology revision
Free revision notes, key terms, common exam traps and 5 practice questions with answers. About 4 minutes to read.
Natural selection
- Variation exists in a population due to genes and environment.
- Individuals with useful alleles survive, reproduce and pass those alleles on.
- Over many generations the population changes — that's evolution.
Selective breeding and GM
- Selective breeding: humans choose parents with desired traits; risk of inbreeding and disease.
- Genetic engineering: a useful gene is cut out and inserted into another organism, e.g. insulin-producing bacteria.
Key terms
- Mutation
- A random change in DNA; most have no effect.
- Speciation
- When populations become so different they can no longer interbreed.
- Selective breeding
- Choosing parent organisms with desired characteristics.
- Variation
- Differences between individuals of the same species, caused by genes and/or environment.
- Selection pressure
- An environmental factor that affects survival chances, e.g. predators, disease, competition.
- Homologous structure
- Similar body structures in different species suggesting a shared ancestor.
Common exam traps
- Saying organisms 'choose' or 'want' to adapt — selection is not deliberate.
- Forgetting the phrase 'over many generations'.
- Saying organisms 'try' or 'choose' to evolve — selection acts on existing random variation, it isn't goal-directed.
Practice questions with answers
1. Explain how antibiotic-resistant bacteria arise.
Answer: A random mutation makes some bacteria resistant; the antibiotic kills the rest, the resistant ones survive, reproduce and pass on the allele.
Mutation → survival → reproduction → spread.
2. Which is a disadvantage of selective breeding?
- • Reduced genetic variation and more inherited disease
- • It is illegal
- • It slows plant growth
- • It causes mutations in humans
Answer: Reduced genetic variation and more inherited disease
Inbreeding reduces the gene pool.
3. Give one benefit of genetic engineering in medicine.
Answer: Bacteria can be modified to produce human insulin in large quantities.
Use a specific example.
4. Charles Darwin's theory of evolution is based mainly on:
- • Natural selection
- • Genetic engineering
- • Selective breeding
- • Cloning
Answer: Natural selection
Darwin proposed that organisms best suited to their environment survive and reproduce.
5. Explain why fossils provide evidence for evolution.
Answer: Fossils show how organisms have changed gradually over long periods of time, showing a sequence of gradual change linking earlier and later species.
The fossil record shows change over geological time.
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