Final answer:
Allelic fixation refers to the scenario where a new allele becomes present in every individual within a population. This occurs through genetic drift or natural selection, with genetic drift being random while natural selection favors alleles that offer an advantage.
Step-by-step explanation:
A new allele that arises in a population and then becomes fixed is known by the term allelic fixation. When an allele becomes fixed in a population, it means that every individual in that population carries that allele. This can occur through several mechanisms including genetic drift, natural selection, or a combination of these processes. Genetic drift, as suggested by Figure 19.4, is the change in the frequency of an allele in a population due to random sampling of organisms, and it can lead to the fixation of alleles purely by chance. Natural selection can also drive alleles to fixation if they confer a survival or reproductive advantage to individuals within the population. For example, the studies of changes in wing coloration in the peppered moth is a classic example of an allele becoming fixed due to natural selection.
When a new allele arises in a population and then becomes fixed, it is known as allele fixation. Allele fixation occurs when a particular allele's frequency increases over time, eventually reaching a frequency of 100% in the population. This can happen through various mechanisms, such as natural selection, genetic drift, or migration.