A population of an annual plant species contains plants with thin leaf wax and plants with thick leaf wax. The difference in leaf wax is inherited.
Thick leaf wax reduces water loss. A drought acts as a selection pressure on the population.
Scientists collect the following data.
| Phenotype | Number of plants at the start | Number of plants that produced seeds | Mean number of viable seeds per plant that produced seeds |
|---|---|---|---|
| Thin leaf wax | 120 | 36 | 25 |
| Thick leaf wax | 80 | 56 | 20 |
Calculate the mean number of viable seeds produced per plant present at the start for each phenotype. Show your working.
Explain how natural selection is likely to change the proportion of the two phenotypes if drought conditions continue for many generations.
After the drought, rainfall is high for many generations. Suggest why the thick-leaf-wax phenotype might not continue to become more common.
122 exam-style questions on OCR GCSE Biology 5.2 Natural selection and evolution, covering 5.2.1 Genetic variation within a population, 5.2.2 Developments in classification systems, 5.2.3 How evolution occurs through natural selection, 5.2.4 Evolution as change over time, 5.2.5 Evidence for evolution, and 5.2.6 Darwin and Wallace. Each one has a worked solution and a mark scheme showing where the marks go.