Biology 9700 · AS & A Level · Natural and artificial selection

Natural and artificial selection — practice question

In rural India, the main way of controlling a species of $Anopheles$ mosquito is to spray insecticide on the inner walls of houses. Several different insecticides have been used. For many years, malathion was the principal insecticide. In 2005, this was replaced by the newer insecticide, deltamethrin, and malathion was no longer used. A laboratory investigation was done with mosquitoes gathered from two sites in India. The proportion of mosquitoes killed by malathion and deltamethrin was estimated. The findings are shown in Table 4.1.
(a)[3]

With reference to Table 4.1, describe how the effectiveness of the two insecticides differs.

(b)[4]

The researchers concluded that at Jamnagar the mosquitoes had evolved resistance to deltamethrin. Explain the way in which the mosquitoes evolved resistance.

(c)[2]

Explain how the data in Table 4.1 provide evidence that malathion use stopped after 2005.

(d)[1]

The resistance of mosquitoes to malathion was found to result from a difference in the shape of one enzyme. Name the type of variation that controls malathion resistance in the mosquito population.

(e)[3]

Some students proposed that malathion resistance could be controlled by a gene with two alleles, and that the allele for resistance to malathion would be dominant over the allele for non-resistance. With this assumption, the data in Table 4.1 can be used to calculate the frequency of resistant mosquitoes and the frequency of the allele for resistance in a mosquito population. Use the Hardy-Weinberg principle to calculate the frequency, $p$, of the allele for resistance in Jamnagar in 2005.

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This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: deltamethrin is more effective overall at killing mosquitoes

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