If two genes for a particular characteristic are dissimilar in nature the genotype of these two genes are called heterozygous. The cell or organism is called a heterozygote specifically for the allele in question, and therefore, heterozygosity refers to a specific genotype.
Explanations: If at cross is made between a pure tall “TT” and a pure dwarf (tt) plant the genotype of the first filial generation (F1) will be “Tt”. Here; genotype of the “Tt” is heterozygous. If an organism is heterozygous for a gene, or possesses one of each allele, then the dominant trait is expressed. A recessive allele is only expressed if an organism is homozygous for that trait, or posses two recessive alleles.