An allele, as you will know, is an alternative form of a gene such as the blue eyed Gene/allele and the dark eyed gene/allele. So an allele is a member of a pair for any given trait that occupies the same specific position on the pairs of homologous chromosomes, that is the matching chromosomes that you inherit ,one from each parent. Inheritance for any trait is purely at random,depending on what your parents have themselves inherited in their genotypes. A diploid cell contains an allele from each parent for any given trait at its own particular locus. This can be either a pair of homozygous dominant alleles(pure breeding dominant) for ,say hair colour, or a pair of homozygous recessive alleles ( pure breeding recessive) or a pair of alternative alleles (different copies) ,called heterozygous. Hope this helps.