A gene which expresses itself both in the heterozygous and homozygous condition is called a/an

A dominant gene expresses its phenotype in both heterozygous (one dominant + one recessive allele) and homozygous (two dominant alleles) conditions. This is why dominant traits appear in offspring even when only one parent carries the dominant allele. Recessive genes only express when homozygous, while codominant genes show both traits simultaneously in heterozygotes.