Technical Definition of an Allele - Alternative form of a genetic locus; a single allele for each locus is inherited from each parent (e.g., at a locus for eye color the allele might result in blue or brown eyes).

Let's think about a gene as being like a page in a book. On this imaginary page are the complete instructions to make a product. Let's also imagine that all individuals of a species have this page in their 'genetic library' (genome). From one individual to the next there may be slight differences in the letters that are on this given page. Let's say, for example, there are 99 letters on the page. All of these letters may be the same from one individual's page to the next. But, there may be one, or a few letters, on the page that may be different from one individual to the next. This variation is called an allele.

If the pages have slightly different letters, but they have the same position in the books from one library to the next (in the same species), then these pages are called alleles. Thus, if two people have pages that are exactly alike they both have the same allele. If there is a slight difference in the page that two individuals, have then they have different alleles. These slight changes in the page may or may not influence what is finally manufactured from the instructions on the page. In some cases these differences can have a big effect on an organism. For example, alleles can influence the color of a rabbit's hair (see below) or the color of a flower.