The mutation in the FBN1 gene that causes Marfan syndrome influences the phenotypic outcomes of several traits in the human body (elongated head, limbs, and digits; lung and eye problems; and heart valve and vessel defects). In your current research you identify a second gene, called FCD3, whose expression is affected by the FBN1 mutation. This scenario of genes interacting with each other to determine phenotype is an example of .

epistasis

Explanation:

Epistasis refers to the genetic mechanism by which the expression of one gene is affected by the expression of other gene/s. In epistasis, two or more genes interact with each other in order to determine a phenotypic trait, thereby a particular gene contributes or masks the expression of other gene/s. In humans, the gene for albinism (absence of melanin pigment) is an example of an epistatic gene that prevents pigment formation and color formation. On the other hand, a pleiotropic gene is a single gene that affects more than one phenotypic trait (e.g., a mutation in a single gene that codes for phenylalanine hydroxylase enzyme results in multiple phenotypes associated with phenylketonuria disorder).

ok

explanation:

"a.) well–developed vascular system."