Pleiotropy (pleiotropy) is a multiple action of a gene; a type of inheritance in which one gene determines the manifestation of several traits.
Most genes have been found to have pleiotropic (multiple) effects. This phenomenon is due to the fact that one gene is associated with several stages of biochemical processes, therefore it affects the development of many properties of the body.
The phenomenon of multiple gene action is common in both plants and animals.
Example: in many plants, a gene that determines the color of a flower causes a change in the color of other organs (stem, leaves, seeds).
Example: in humans, a mutant gene that controls the development of connective tissue causes spider fingers syndrome (Marfan syndrome) and causes not only lengthening of the fingers and toes, but also a change in the shape of the face, lens defect, congenital heart defects, etc.
Example: The gene for red hair also causes lighter skin coloration and freckles.