Natural Selection · Paper 1 — Free Biology HL Practice Questions

In a population of guppies (Poecilia reticulata), males with more orange spots gain greater mating success due to female preference, but also suffer higher predation rates. Which type of natural selection best describes the combined effect of these two opposing pressures on the number of orange spots in males?

In a meadow, grasshoppers vary in colour from bright green to brownish-green. During a prolonged drought, dry brown patches replace most of the green grass. A biologist records that the proportion of brownish-green grasshoppers increases significantly over several generations. Which of the following best explains this change in allele frequency?

In a population of 500 moths living in a forest with dark-coloured tree trunks, moth colour is controlled by a single gene with two alleles. The dark allele ($D$) is dominant over the light allele ($d$). Of the 500 moths, 180 are light-coloured. Assuming Hardy–Weinberg equilibrium, what is the frequency of the allele $d$?