Final answer:
A gene that has a role in multiple biochemical pathways is described as C. pleiotropic. This concept of pleiotropy is distinct from dominance patterns in genetics, such as dominant, recessive, codominance, and incomplete dominance, which refer to how different alleles of a gene influence the phenotype.
Step-by-step explanation:
A gene that produces a protein important in more than one biochemical pathway is pleiotropic. Pleiotropy occurs when one gene influences multiple phenotypic traits. This is not to be confused with the terms dominant, recessive, codominant, or incomplete dominance, which describe how traits are expressed when different versions (alleles) of a gene are present.
Multiple alleles and codominance are illustrated by the ABO blood group system. In this case, alleles IA and IB are codominant, meaning that when both are present, both are expressed, as seen in blood type AB. However, both IA and IB are dominant over allele i, which results in blood type O when in homozygous form (ii).
In the context of dominance, a dominant allele is one that will express its trait or gene product whether it is in homozygous ('AA') or heterozygous ('Aa') form. It is important to remember that the physical expression, or phenotype, is dependent on the combination of alleles inherited, not just on whether a single allele is dominant or recessive.