An allele is a variant form of a gene that arises by mutation and is located at a specific position on a specific chromosome. Alleles occur in pairs (one inherited from each parent) and can either be dominant or recessive. Dominant alleles are expressed and determine the physical characteristics or traits of an organism, while recessive alleles are only expressed if the individual has two copies of the recessive allele. Alleles are responsible for the genetic diversity and inheritance patterns observed in populations.
