A canyon separated a population of lizards into populations X and Y. Birds prey on lizards in both populations. The lizards have either dark or pale skin, and one allele causes dark skin.
The table shows data collected from the two populations.
| Population | Colour of rocks | Dark lizards eaten by birds (%) | Pale lizards eaten by birds (%) | Lizards carrying the dark-skin allele in generation 1 (%) | Lizards carrying the dark-skin allele in generation 25 (%) |
|---|---|---|---|---|---|
| X | Dark | 12 | 46 | 28 | 72 |
| Y | Pale | 54 | 17 | 31 | 9 |
Use the data and your knowledge of natural selection to explain why the percentage of lizards carrying the dark-skin allele changed differently in populations X and Y.
After many more generations, scientists crossed lizards from the two populations. Further breeding tests were carried out on every offspring to determine whether each offspring was fertile.
| Parents | Number of offspring produced | Number of offspring shown by further breeding tests to be fertile |
|---|---|---|
| Population X × population X | 40 | 34 |
| Population Y × population Y | 38 | 32 |
| Population X × population Y | 26 | 0 |
All offspring not shown to be fertile in the final column were found to be infertile.
Use the results to explain why the scientists classified populations X and Y as two different species.
80 exam-style questions on AQA GCSE Biology 6.2 Variation and evolution, covering 6.2.1 Variation, 6.2.2 Evolution, 6.2.3 Selective breeding, 6.2.4 Genetic engineering, and 6.2.5 Cloning. Each one has a worked solution and a mark scheme showing where the marks go.