In a heterozygous allele pair, one dominant and one recessive allele for a trait are present in a person's genotype. Therefore it is the recessive allele that is not expressed.
When a person is heterozygous for a particular trait, in general the dominant trait is expressed. The classic example of this is pea plant height from Mendelev's experiments - a pea plant that...
If it's not a heterozygous, the alleles would either be two capital letters (TT) or two lowercase letters (tt). This is because the organism has either both two dominant alleles or two recessive...