A specific gene that has identical alleles on both homologous chromosomes is said to be homozygous.
When both alleles are dominant, the genotype is referred to be homozygous dominant.
For instance, a single gene with two alleles controls the height of pea plants; the tall allele (T) is dominant and the short allele (t) is recessive. The homozygous condition will be tall(TT) and dwarf(tt)
Heterozygous
A unique gene in an organism with two different types of alleles is said to be heterozygous.
When an organism inherits a unique gene of a different kind from each of its parents, it is said to be heterozygous.
If an organism is "heterozygous" for a specific trait, it has two alleles (for example, "Aa"), one of which is dominant and the other recessive.
According to Mendel's Law of Dominance, the allele that expresses itself is the dominant allele.