An allele is a variant form of a gene that is found at a specific location on a chromosome. Genes are responsible for determining traits in living organisms, and alleles can influence characteristics such as eye color, hair type, and height. Each individual inherits two alleles for each gene, one from each parent, which can be the same or different. Alleles can be classified as dominant or recessive. A dominant allele will express its trait even if only one copy is present, while a recessive allele requires two copies to show its effect. This genetic variation is essential for evolution and contributes to the diversity seen in species.