QUESTION 10 (3 marks)
Researchers measured the adult beak lengths of an entire population of a species of bird and plotted their results on the graph. After many generations, the lengths of the adult beaks were again measured. By comparing this new data to the original data, the researchers concluded that the average length of beaks had increased as a result of directional selection.
a) Describe directional selection.
[2 marks]
b) On the graph provided, sketch a representation of directional selection for the beak length scenario.
[1 mark]
Note: If you make a mistake on the graph, cancel it by ruling a single diagonal line through your work and use the additional graph on page 17 of this question and response book.
QCAA guide · typeset solution
QCAA sample response and mark allocation
10 | a) | Directional selection is a mode of natural selection in which an extreme phenotype is favoured over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype. | • states directional selection as when an extreme phenotype is favoured in a population [1 mark] population shifts to have more individuals with the phenotype [1 mark] | |
10 | b) | • sketch indicates shift to longer beak length [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.