Fig. 1 shows a phylogenetic tree prepared from DNA sequences of four species of finch on neighbouring islands. Species W and X have similar beak shape, but ...
Question 1 Report
Fig. 1 shows a phylogenetic tree prepared from DNA sequences of four species of finch on neighbouring islands. Species W and X have similar beak shape, but their DNA sequences differ at more bases than species X and Y. The researchers collected small feather samples without harming the birds. They compare DNA sequence differences with observations of the birds' food sources. On one island, a new hard seed plant has spread. Researchers predict that birds with inherited variation in beak depth may not all survive equally well if the food supply changes.
(a) Use Fig. 1 to name the species most closely related to X. [1]
(b) Describe how comparing DNA base sequences can provide evidence for evolutionary relationships. [2]
(c) Suggest how a hard-seed food source could change allele frequencies for beak depth in the finch population. [3]
Answer Details
Labelled answer diagram:
(a) The species most closely related to X is W [1], because W and X share the most recent branching point on the phylogenetic tree.
(b) Species with more similar DNA base sequences have fewer base differences [1]. This indicates that they share a more recent common ancestor and so have a closer evolutionary relationship [1]. Similar beak shape alone is less reliable evidence because similar features can evolve under similar selection pressures.
(c) Finches with deeper beaks can break hard seeds more effectively [1]. They are more likely to survive and reproduce [1], so alleles for deeper beaks are passed to offspring and increase in frequency in the population [1].
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