Fruitflys of the genus Drosophila include many species. Three of these, Drosophila pseudoobscura, D. persimilis and D. miranda, are believed to be closely allied. Specimens of these three species were taken from the western United States of America. Fig. 5.1 indicates their natural distributions. The base sequences of four DNA regions from each species were determined. The divergence in the base sequences of D. pseudoobscura and D. persimilis relative to the sequences in D. miranda was calculated. Table 5.1 shows the results.
(a)[2]
Using Table 5.1 as evidence, describe why D. miranda may be more closely related to D. persimilis than to D. pseudoobscura.
(b)[2]
Suggest why divergence is greater in some DNA regions than in others.
(c)[4]
The region inhabited by D. pseudoobscura is cut off from the regions occupied by the other two species by a high mountain range. Explain how D. pseudoobscura could have evolved from a population of D. miranda.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Smaller divergence values for $D.$ persimilis than $D.$ pseudoobscura” …