A population of small fish has inherited variation in body colour. The water in their habitat becomes darker, and predatory birds catch more of the fish that are easier to see. Which outcome is most likely after many generations?
Alleles for less visible colours become more common, because those fish more often survive to breed.
Colour alleles stay at the same frequency, because birds remove individual fish rather than alleles.
The fish become less visible within their lifetime, because they need to hide from the birds.
The darker water causes new mutations for less visible colours in the fish already alive.
85 exam-style questions on Edexcel GCSE Biology 4.1 Evolution and natural selection, covering 4.1.1 Work of Darwin and Wallace and 4.1.2 Resistant organisms and evolution. Each one has a worked solution and a mark scheme showing where the marks go.