Continuity of life on Earth — Question 11

11a)

$\mathrm{F}\mathrm{r}\mathrm{e}\mathrm{q}\mathrm{u}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}\,(\mathrm{a})\,=\,[(2\,\mathrm{x}\,226)\,+\,60]\,/\,600\,$

$=\,0.85\,$

$\mathrm{F}\mathrm{r}\mathrm{e}\mathrm{q}\mathrm{u}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}\,(\mathrm{A})\,=\,[(2\,\mathrm{x}\,14)\,+\,60]\,/\,600\,$

$=\,0.15\,$

• provides appropriate working [1 mark]

• calculates the frequencies of both alleles [1 mark]

11b)

Allele frequencies remained relatively constant in forest X over the 10-year period, with a slight increase in allele A over time. This suggests genetic drift is occurring and the changes are likely due to chance rather than the environment favouring a particular phenotype. This contrasts with forest Y, where the frequency of allele A increases significantly over time after it first appears in 2016. The allele may have been introduced to forest Y due to migration (mice moving in from a neighbouring forest) or mutation. Either way, it is evident that the allele A provided a selective advantage to mice in forest Y, resulting in its frequency increasing over time.

• identifies allele frequencies remain relatively constant in forest X over time [1 mark]

• infers a reason for the temporal change in forest X [1 mark]

• identifies allele A first appeared in forest Y in 2016 [1 mark]

• infers this is due to migration (gene flow) or mutation [1 mark]

• identifies the frequency of allele A increases over time in forest Y [1 mark]

• infers allele A provides a selective advantage to mice in forest Y [1 mark]