Allelic variation refers to the presence of different forms of genes (alleles) in a population. These alleles are responsible for the diversity of traits among individuals. The primary source of allelic variation is mutation. Let's understand this in detail.

Mutation as the primary source of allelic variation:
Mutation is a permanent change in the DNA sequence that can occur spontaneously or due to exposure to mutagens. It is the ultimate source of genetic variation in a population. Mutations can occur in different ways:

1. Point mutations: These involve a change in a single nucleotide of DNA. They can be of three types:

- Silent mutation: The change in the nucleotide does not result in a change in the amino acid sequence of the protein encoded by the gene.
- Missense mutation: The change in the nucleotide results in a change in the amino acid sequence of the protein.
- Nonsense mutation: The change in the nucleotide creates a premature stop codon, resulting in a truncated protein.

2. Chromosomal mutations: These involve changes in the structure or number of chromosomes. They can be of several types, including:

- Deletion: Loss of a part of a chromosome
- Duplication: Presence of an extra copy of a part of a chromosome
- Inversion: Reversal of the order of a segment of a chromosome
- Translocation: Movement of a segment from one chromosome to another

3. Insertion or deletion of nucleotides: These involve the addition or removal of one or more nucleotides from the DNA sequence, resulting in a frameshift mutation.

These mutations can occur in gametes (sperm or egg cells) and can be passed on to the next generation, resulting in allelic variation.

Other sources of allelic variation:
Apart from mutation, other sources of allelic variation include:

- Recombination: The shuffling of genetic material during meiosis can result in the creation of new combinations of alleles.
- Independent assortment: The random distribution of homologous chromosomes during meiosis can also lead to the creation of new combinations of alleles.
- Polyploidy: The presence of more than two sets of chromosomes (triploid, tetraploid, etc.) can result in the creation of new alleles due to gene duplication and subsequent mutation.

Conclusion:
In conclusion, mutation is the primary source of allelic variation in a population. Other sources such as recombination, independent assortment, and polyploidy can also contribute to the creation of new alleles.