What is the difference between gene and an allele

A gene is a stretch of DNA or RNA that determines a certain trait. Genes mutate and can take two or more alternative forms; an allele is one of these forms of a gene. For example, the gene for eye color has several variations (alleles) such as an allele for blue eye color or an allele for brown eyes.

An allele is each of the two or more versions of a gene. An individual inherits two alleles for each gene, one from the father and the other from the mother. The alleles are in the same position within the homologous chromosomes ... Instead, if the alleles are different, the individual is heterozygous for this gene.