Explanation:
Allelic variation is a term used to describe the genetic differences that exist between individuals within a population. These differences arise due to mutations, which are changes that occur in the DNA sequence of an organism's genome. Mutations can occur spontaneously, as a result of errors during DNA replication or repair, or they can be induced by mutagens such as radiation or chemicals.

Mutations are the ultimate source of allelic variation because they introduce new genetic material into a population. This new genetic material can then be subject to natural selection, genetic drift, and recombination, which can further shape the genetic diversity of a population over time.

The impact of mutations on allelic variation can be quite diverse. Some mutations may be beneficial, leading to new adaptations that increase an organism's fitness in its environment. Other mutations may be neutral, having no effect on an organism's phenotype or fitness. Finally, some mutations may be deleterious, causing harm to an organism's health or survival.

In summary, mutations are the ultimate source of allelic variation in a population. They introduce new genetic material that can then be subject to various evolutionary forces, shaping the genetic diversity of a population over time.