In population genetics, what is the typical long-term effect of advantageous variants?

• A. They become more frequent in the population.
• B. They cause immediate speciation.
• C. They disappear from the population.
• D. They have no effect on allele frequencies.

Answer: (A)

The key idea here is that natural selection favors alleles that increase fitness. When a variant provides a reproductive advantage, individuals carrying it leave more offspring, so that allele becomes more common in the population over generations. Over the long term, a strongly beneficial allele is likely to rise in frequency and often reach fixation, meaning it becomes present in nearly all individuals, as long as the environment remains favorable and other forces like drift, migration, or new mutations don’t counteract it. This is not about causing immediate speciation or disappearing overnight; speciation is a separate, longer process involving the development of reproductive barriers. The allele does have an impact on allele frequencies, increasing them instead of leaving them unchanged or eliminating the variant.