In Mendel's principle of dominance a recessive gene will always be masked by a dominant gene. In Mendelian genetics each organism's traits are controlled by two alleles (forms of a single gene). When both alleles are dominant the organism will exhibit the dominant trait. When one allele is dominant and the other is recessive, the organism will still display the dominant trait. When the organisms has two recessive alleles, only then will you see the recessive trait. The reason the organism has two alleles, is one comes from the organism's mother and the other from the father.
