Which of the following is an example of pleiotropy in humans?

• A. Marfan syndrome affecting multiple physical traits
• B. Color blindness linked to one gene
• C. Height influenced by multiple genes
• D. Blood type determined by one gene

Answer: (A)

Pleiotropy refers to a phenomenon where a single gene can influence multiple, seemingly unrelated phenotypic traits. In the case of Marfan syndrome, which is caused by a mutation in the FBN1 gene, the effects of this gene extend to various systems in the body, including the skeletal system, cardiovascular system, and the ocular system. Individuals with Marfan syndrome may exhibit tall stature, long limbs, and issues with heart valves or eye lens dislocation, showcasing how one genetic alteration can lead to a range of physical manifestations.

The other options provided illustrate different genetic concepts. Color blindness, while caused by a single gene, primarily affects vision and does not have the broad, varied effects characteristic of pleiotropy. Height is an example of polygenic inheritance, where multiple genes contribute to the trait, rather than one gene having multiple effects. Blood type, determined by a single gene, also affects only a specific characteristic (the ABO and Rh blood group) without impacting multiple bodily systems. Thus, Marfan syndrome is a clear and definitive illustration of pleiotropy in humans.