In a population of 500 beetles, 320 are green and 180 are brown. If green colour is determined by allele G and brown by allele g, and the population is in Hardy-Weinberg equilibrium, what is the approximate frequency of the recessive allele g?

Under Hardy-Weinberg equilibrium, the frequency of homozygous recessive individuals (gg) = 180/500 = 0.36, which equals $q^2$. Therefore $q = \sqrt{0.36} = 0.60$. Wait — this gives q = 0.60 for the recessive allele. However, if brown beetles (180) are recessive: $q^2 = 0.36$, so $q = 0.60$. The frequency of allele g is 0.60. Re-checking: answer should be B (0.60). Correction applied — the frequency of the recessive allele g = $\sqrt{0.36}$ = 0.60.