The difference between dominant and recessive traits is that: the dominant trait the allele found in the parent has an major effect to determine the characteristics even if it is only one of the alleles, while the recessive trait is absent or not exoressed if it is not found in homozygosity. The molecular explanation of this situation is that the relationship between two alleles is important for determine the phenotipical character of an organism, being the one that is present in the individual (in a heterozygote gene) dominant over the other allele that is called recessive (because, even if it is present in the genotype of the organism, it is not expressed as a phenotype).