<prompt> Single gene defect causing multiple unrelated problems is known as:PleiotropismPseudodominancePenetranceAnticipation  <response>: Pleiotropism refers to the phenomenon in which a single mutant allele having widespread effects or expression in different tissues or organ systems. Eg is Marfans syndrome caused by a mutation in fibrillin gene causing multiple manifestations. Penetrance refers to the propoion of individuals with a paicular genotype that express the same phenotype. Penetrance is said to be complete when 100 of mutant individuals express the phenotype. Penetrance is incomplete when some mutant individuals do not express the phenotype. Ref: Tsaic A.C., Manchester D.K., Elias E.R. 2012. Chapter 37. Genetics Dysmorphology. In W.W. Hay, Jr., M.J. Levin, R.R. Deterding, J.J. Ross, J.M. Sondheimer Eds, CURRENT Diagnosis Treatment: Pediatrics, 21e. 