Comparison of heterozygous and zygous alleles?

When the alleles are identical, the individual is zygous for that trait. While if the pair is made of two different alleles, the individual is heterozygous. A zygous pair of can be either dominant (AA, BB) or recessive (aa, bb). Heterozygous pairs are made up of one dominant and one recessive allele (Aa, Bb). In heterozygous individuals only one allele, the dominant, gains expression while the other allele, the recessive, is hidden but still present. Capital letters represent dominant genes and lower case letters, recessive genes. The word genotype is was created to identify genes of an individual and phenotype for the expression of the trait and genes. Phenotype and genotype are terms used to describe the difference between the visible expression of the trait vs. the actual gene makeup. An individual which expresses a dominant trait may carry a recessive allele, but the recessive expression is hidden by it's dominant partner.