noun, plural: alleles
In humans, simple traits such as eye color may be caused by the interaction of only one pair of alleles. But for complex traits, such as height, they are usually caused by the interactions of series of alleles. Some alleles are dominant over other alleles, as in the case of heterozygous pairings (where paired alleles are different, in contrast to homozygous pairings where alleles are the same). In the above example, since the alleles code for different eye colors they are heterozygous.
Colloquially, the term gene is used when referring to an inherited trait that is usually accompanied by a phenotype as in ‘tall genes’ or ‘bad genes’ – but the more proper (scientific) term for this is allele.