What is a gene and what is an allele

Gene - a unit of heredity that is transferred from a parent to an offspring and is held to determine some characteristics of the offspring.

allele - one of 2 or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

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.