Explain the mechanism of evolution according to the modern synthetic theory.

1. 1 · State the theory in one line. The modern synthetic theory explains evolution as a change in allele frequencies in a population over generations, combining natural selection with genetics.
2. 2 · Explain the sources of variation.
   • Mutation: sudden heritable change; random and directionless (de Vries, evening primrose).
   • Recombination: crossing over and independent assortment in meiosis give new combinations.
3. 3 · Explain gene flow and genetic drift. Gene flow: repeated migration of alleles between populations. Genetic drift: chance change, with the founder effect in small groups.
4. 4 · Explain natural selection. Variants that survive better leave more progeny, so useful alleles increase.
5. 5 · Add speciation. Selected changes build up over generations and can lead to speciation. Extra, beyond the textbook: reproductive isolation stops the groups interbreeding.
6. 6 · Show the flow. [Flow chart: mutation and recombination, variation, change in allele frequency, isolation, new species]
7. 7 · Close in one line. So variation supplies the raw material and selection and drift shape it into new species.

Scoring tip: Use the phrase 'change in allele frequency'. It shows the examiner you understand the population view of evolution.