Which characteristics show complete dominance on a human?

Complete dominance in humans occurs when one allele completely masks the expression of another allele for a particular trait. An example of this is the ABO blood group system, where the A and B alleles are dominant over the O allele; thus, individuals with AO or BO genotypes will express the A or B blood type, respectively. Other traits displaying complete dominance include the presence of attached or free earlobes, where the allele for free earlobes is dominant over the allele for attached earlobes. In both cases, the dominant allele's phenotype is fully expressed in the presence of a recessive allele.