Pleiotropy just means that one gene is involved in many different phenotypes. An example of this is the the CFTR gene, which when mutated causes cystic fibrosis. Cystic fibrosis is a disease which is characterized by the perturbation of multiple systems, including the lungs, liver, pancreas, kidneys, and bowel. Epistasis is refers to the interaction of multiple genes (two or more loci) in determining a phenotypic outcome.
