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

Natural and artificial selection — practice question

The principal way of controlling a species of $\textit{Anopheles}$ mosquito in rural India is to spray insecticide onto the interior walls of houses. Several different insecticides have been used. For many years, malathion was the main one. In $2005$, this was replaced by the newer insecticide deltamethrin, and malathion use stopped. A laboratory investigation was done with mosquitoes collected 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]

Using Table 4.1, describe how the effectiveness of the two insecticides differs.

(b)[4]

The researchers concluded that the Jamnagar mosquitoes had evolved resistance to deltamethrin. Explain the process by which this resistance evolved.

(c)[2]

Explain how the data in Table 4.1 indicate that malathion use was discontinued after 2005.

(d)[1]

The resistance of mosquitoes to malathion was found to be due to 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 suggested that malathion resistance might be controlled by a gene with two alleles. They proposed that the resistance allele would be dominant over the non-resistance allele. With this assumption, the data in Table 4.1 can be used to work out the frequency of resistant mosquitoes and the frequency of the resistance allele 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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