Defective colour vision is more common among males than females because
A) males have fewer cones than females.
B) genes for photopigments are carried on the Y chromosome.
C) as a result of higher estrogen levels, females produce more rhodopsin than males.
D) genes for photopigments are carried on the X chromosome.
E) as a result of lower estrogen levels, males produce more rhodopsin than females.

Question

Quizplus · Accepted Answer

Defective color vision is more common among males because the genes responsible for the most common forms of color blindness are located on the X chromosome. Males have only one X chromosome (XY), while females have two (XX), so a defective gene on one of a female's X chromosomes can be compensated for by a normal gene on the other, but males have no such backup.

Defective Colour Vision Is More Common Among Males Than Females