At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus.
Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
Okay, so an allele is a part of your DNA that codes for a specific trait (say hair colour) there are usually two different alleles that code for the trait (eg. Red hair and Brown Hair - but there a sometimes more, like in the case of hair) and which alleles you have changes what traits are shown (in other words if you have 2 alleles for red hair you will have red hair).
Hmmmm Have I overcomplicated that?
if you think of a punnet square, the alleles are the letters that you would use to define a trait, such as Aa X AA. the big a here is the dominant allele and the small a is the recessive allele. But alleles are what you inherit from your parents.
so they are two genes which control the same phenotype, right???
Not the answer you are looking for? Search for more explanations.
Essentially, however there can be more than two that control it (like blood types which has three alleles)
An allele is one of two or more forms of genes (generally a group of genes). Sometimes, different alleles can result in different traits, such as color. At other times, different alleles give rise to the same trait, since some variations at the genetic level result in little or no variation of a trait.
Most multicellular organisms have two sets of chromosomes, that is, they are diploid. These chromosomes are referred to as homologous chromosomes. Diploid organisms have one copy of each gene (and therefore one allele) on each chromosome. If both alleles are the same, they are homozygotes. If the alleles are different, they are heterozygotes.