Selection and changing allele frequenciesAQA A-Level Biology: Mind map

Exam questions on Selection and changing allele frequencies

1. On a hospital ward, a population of bacteria is exposed to an antibiotic. Before treatment, a very small proportion of the bacteria carried an allele that makes them resistant to the antibiotic.
   Explain how the frequency of the resistance allele in the bacterial population increases after the antibiotic is used.2 marks
2. In human populations, babies with a birth weight close to the population mean of about 3.3 kg have the highest rate of survival. Babies with a very low or very high birth weight have a higher death rate.
   Explain the effect of this type of selection on the frequencies of the alleles affecting birth weight.2 marks
3. On a small island, seed-eating birds feed on seeds of different sizes. Beak depth varies widely between individual birds and is partly inherited. During a severe drought, the plants producing small, soft seeds died, leaving mainly large, hard seeds. After the drought, the mean beak depth of the next generation of birds was greater than before.
   Explain how the drought led to an increase in the mean beak depth of the birds in the next generation.3 marks