Here's why:

* Locus: A specific location on a chromosome where a gene resides.

* Genes: Units of heredity that determine specific traits.

* Alleles: Different versions of the same gene.

When two different alleles (versions) of the same gene occupy the same locus, they are considered allelic variations. This variation leads to the expression of different phenotypes, or observable characteristics.

For example:

* Eye color: The gene for eye color has multiple alleles, such as blue, brown, and green. Different combinations of these alleles at the same locus determine the resulting eye color.

Let me know if you'd like more examples or a deeper dive into genetics!