What are heterozygous and homozygous alleles and when will they show?

Heterozygous alleles are when a dominant and recessive allele are present in the phenotype such as Ee. While homozygous alleles are when two of the same alleles are present in the phenotype e.g. ee or EE. Because dominant alleles will always show when present, recessive alleles will only show when alleles are homozygous.