A gene is said to be dominant if

1. it expresses its effect only in homozygous state
2. it expresses its effect only in heterozygous condition
3. it expresses its effect both in homozygous and heterozygous condition
4. it never expresses its effect in any conditions

A dominant gene would lead to the expression of its phenotype irrespective of the fact whether its allelic gene is dominant or recessive.