Some populations of monkeyflower (Mimulus guttatus) can survive in soils with high concentrations of copper due to a copper-tolerance allele. This phenotypic trait is genetically determined.
Scientists conducted a field-selection study over two successive generations in an area adjacent to a newly opened copper mine to investigate how the frequency of copper-tolerant plants changes. Their observed results for the initial colonising population (Generation 0) and the subsequent generation (Generation 1) are shown in the table below:
| Generation | Observed: Sensitive to copper | Observed: Tolerant to copper |
|---|---|---|
| 0 | 160 | 40 |
| 1 | 140 | 60 |
The scientists want to use a chi-squared (χ2\chi^2χ2) statistical test to evaluate their results. They set up the following null hypothesis:
'The proportion of plants that are tolerant to copper will not change from Generation 0 to Generation 1.'
Calculate the expected number of plants of each phenotype in Generation 1 under the null hypothesis.
Calculate the chi-squared (χ2\chi^2χ2) value for Generation 1.
The critical value of χ2\chi^2χ2 at P=0.05P = 0.05P=0.05 (with 1 degree of freedom) is 3.8413.8413.841. State whether the null hypothesis should be accepted or rejected, and explain what this indicates about the probability that the observed differences arose by chance.
21 exam-style questions on AQA A Level Biology Investigating diversity. Each one has a worked solution and a mark scheme showing where the marks go.