What term describes many characteristics that are controlled by the same gene?

The correct term for many characteristics that are controlled by the same gene is "pleiotropic." This concept in genetics refers to the phenomenon where a single gene influences multiple phenotypic traits. For example, mutations in a single gene can result in a variety of effects on an organism's development, physiology, or behavior. This is significant in understanding how certain genetic disorders can manifest in diverse ways, impacting multiple systems within the body.

Other terms presented in the choices have specific meanings but do not capture this particular concept. Polygenic refers to traits that are influenced by multiple genes, which results in a wide range of phenotypes rather than multiple effects from a single gene. Multiphenic is not a standard term used in genetics related to gene influence and is likely a misnomer. Phenotypic simply refers to the observable traits that result from the interaction of genetics and environment, but does not specifically denote the relationship of a single gene controlling multiple traits. Thus, pleiotropic is the term accurately describing how one gene can have multiple influences on an organism.