CAIE A Level Biology 9700 · Selection and evolution
The table below shows the percentage similarity in DNA sequence between three species of flowering plants, A, B, and C.
| Species A | Species B | Species C | |
|---|---|---|---|
| Species A | 100% | 92% | 78% |
| Species B | 100% | 81% | |
| Species C | 100% |
Outline how such DNA sequence data can be used to show evolutionary relationships between species, and explain how speciation, resulting in differences like those shown, may occur through allopatric and sympatric isolation.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Outline means: Give the main points briefly. Less detail than describe, but every key step has to be there. One short line per step, in order. The marks are for coverage, not depth.
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