A species of marine worm lives only in warm water around a chain of vents on the sea floor. Several vents in the middle of the chain stop releasing warm water. This leaves a wide area of cold water that the worms cannot cross, separating the northern and southern populations.
Bristle length in the worms is an inherited characteristic controlled by alleles.
The table shows results after the populations have been separated for 18 generations.
| Population | Short-bristled worms surviving to breeding age (%) | Long-bristled worms surviving to breeding age (%) | Short-bristled young worms in generation 1 (%) | Short-bristled young worms in generation 18 (%) |
|---|---|---|---|---|
| Northern | 76 | 45 | 38 | 69 |
| Southern | 42 | 73 | 40 | 17 |
Explain why the percentage of short-bristled young worms changed in opposite directions in the two populations.
Scientists carried out breeding tests using worms from the two populations.
| Time of breeding test | Offspring from northern × southern parents that were tested | Offspring that later produced offspring themselves |
|---|---|---|
| Generation 20 | 24 | 20 |
| Generation 200 | 17 | 0 |
Use the results to explain whether the northern and southern populations were separate species at generation 20 and at generation 200.
Scientists could restart the vents between the northern and southern populations, allowing the worms to meet again.
Predict how restarting the vents at generation 20 would affect further divergence compared with restarting them at generation 200.
71 exam-style questions on AQA GCSE Biology 6.3 The development of understanding of genetics and evolution, covering 6.3.1 Theory of evolution, 6.3.2 Speciation, 6.3.3 The understanding of genetics, 6.3.4 Evidence for evolution, 6.3.5 Fossils, 6.3.6 Extinction, and 6.3.7 Resistant bacteria. Each one has a worked solution and a mark scheme showing where the marks go.