Dominance relationships govern how the alleles at the same gene locus on homologous chromosomes interact to produce the phenotype. There can be a degree of subtlety in dominance relationships beyond the simplisticly interacting alleles of Mendel's peas. On the new MCAT, with its heightened emphasis on genetics, subtle dominance relationships would be an ideal topic to be explored within a passage. In the case of a heterozygous genotype, one copy of the dominant allele may be enough for the development of a normal phenotype. However, it is often the case that a single allele does not lead to the creation of sufficient active gene product to create the dominant phenotype. This is called incomplete dominance.