Which X-linked disorder is characterized by an inability to distinguish red from green?

Which X-linked disorder is characterized by an inability to distinguish red from green?

• A. Qualitative variation
• B. Polygenic traits
• C. Pleiotropy
• D. Red-green color blindness

Answer: (D)

This item tests an X-linked color-vision deficiency, specifically red-green color blindness. It arises from mutations in the opsin genes on the X chromosome that encode the photopigments in the long- and medium-wavelength cones; when these pigments don’t function normally or their spectral sensitivities overlap, distinguishing red from green becomes difficult or impossible. The inheritance is usually X-linked recessive, so males are more often affected because they have only one X chromosome, while females are typically carriers with normal color vision since they have a second, normal X. Occasionally, due to X-inactivation, carrier females can show mild impairment. The other terms describe broader genetic concepts rather than naming a specific X-linked disorder of color vision.

This item tests an X-linked color-vision deficiency, specifically red-green color blindness. It arises from mutations in the opsin genes on the X chromosome that encode the photopigments in the long- and medium-wavelength cones; when these pigments don’t function normally or their spectral sensitivities overlap, distinguishing red from green becomes difficult or impossible. The inheritance is usually X-linked recessive, so males are more often affected because they have only one X chromosome, while females are typically carriers with normal color vision since they have a second, normal X. Occasionally, due to X-inactivation, carrier females can show mild impairment. The other terms describe broader genetic concepts rather than naming a specific X-linked disorder of color vision.