The blackcap, $\textit{Sylvia atricapilla}$, is a small songbird. It is a summer visitor to parts of northern Europe, where it breeds.
Many blackcaps pass the winter (overwinter) in southern Europe, especially Spain. Because many people put out food for garden birds, some birds are able to survive the winter in the UK.
Scientists compared the genetic variation between blackcaps from two forest sites in Germany, $800\,\text{km}$ apart. Both sites had birds that had overwintered in Spain and in the UK. The measurements were taken soon after the birds returned from their winter feeding grounds.
(a)[4]
Explain how DNA sequencing may be used to measure genetic variation in birds.
(b)
The genetic variation measurements showed that:
• birds that overwinter in the same country (Spain or the UK) had many alleles in common, even though in summer they were living $800\,\text{km}$ apart in Germany
• birds that overwintered in different countries (Spain or the UK) shared fewer alleles, even though in summer they were living in the same forest in Germany
• the genetic differences among the birds that overwinter in Spain imply that they no longer breed with the birds that overwinter in the UK.
(c)[4]
Explain how these blackcaps could evolve into two separate species.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The DNA is denatured.” …