Final answer:
Over hundreds of generations, allele frequency in a population can change due to natural selection or genetic drift, potentially leading to beneficial alleles becoming fixed or certain alleles fluctuating in frequency due to random chance, especially in small populations.
Step-by-step explanation:
Over a long period of time (hundreds of generations), the allele frequency in a population can change due to various evolutionary factors, including natural selection and genetic drift. Natural selection occurs when alleles that confer a survival or reproductive advantage increase in frequency as they are more likely to be passed down to subsequent generations. This can lead to beneficial alleles becoming fixed within a population, whereas deleterious alleles may be eliminated. On the other hand, genetic drift is a random process that impacts allele frequencies, especially in small populations. Chance events can cause certain alleles to be more common in the next generation, regardless of their effect on fitness.
For instance, an individual's alleles may not be passed on simply because of random mortality or mating events. Over many generations, these random changes can lead to significant shifts in the gene pool, the sum of all alleles within a population. In a smaller population, the effect of drift on allele frequencies is more pronounced, potentially leading to fixation of alleles purely by chance even if they don't confer an evolutionary advantage.