If two populations are merged, each with different frequencies of an allele at a locus, and randomly mating occurs immediately, how long will it take to achieve a Hardy-Weinberg equilibrium in the new population?

When two populations with different allele frequencies merge and begin random mating, Hardy-Weinberg equilibrium is achieved in just one generation. Random mating in the first generation immediately creates the genotype proportions predicted by HWE, based on the new combined allele frequencies. No additional generations are needed.