Alleles are different versions of a gene. A gene is the piece of DNA which carries information in the form of a sequence of amino acids. For every gene that we have, we carry 2 alleles which could be the same or could be two different types. alleles can be dominant or recessive. for example, the allele for brown eyes is dominant and so if you have one copy of the brown eye allele and one of the blue eye you will have brown eyes as it dominates over the blue eye allele. alternatively, if you have two of the blue eye alleles you will have blues eyes as this allele requires two of the same allele to present!