Q118 · Practice questionComplex familiar1 mark
QUESTION 118
A resistance allele is detected in stored DNA from a population sampled before a particular pesticide was first used there. After pesticide use begins, individuals carrying the allele leave more offspring and its frequency increases. Which explanation is best supported?
(A)
Selection increased the frequency of a pre-existing allele.
(B)
The pesticide must have directed the first mutation that produced this allele.
(C)
The allele first appeared only after the pesticide was applied.
(D)
Individuals changed the DNA sequence of every allele because they needed resistance.
WORKED SOLUTION
1 markAnswer A
Answer
A
Working
The stored sample establishes that the allele existed before the pesticide exposure. The later reproductive advantage is consistent with selection increasing the frequency of an existing variant; it does not show that the pesticide created a needed mutation.
Marking criteria
- Select A. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
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