What is Allele?

An allele is a variant of a gene that can exist at a single locus (position) on a chromosome and code for a different trait variation. 

For example, there may be two alleles at the locus controlling flower colour in pea plants: one for purple flowers (P) and one for white flowers (W) (p). 

When an organism inherits two copies of the same allele (for example, PP or pp), it is said to be homozygous for that trait, whereas when it inherits two different alleles (for example, Pp), it is said to be heterozygous. 

An organism's phenotype is determined by the combination of alleles it possesses as well as the environment.