Question

Opsins are proteins that are found in the light-sensing cells in the human eye. Different opsin proteins are sensitive to different colors of light. The instructions for creating the type of opsin sensitive to red light are found on a gene known as OPN1LW, which is on the X chromosome. A genetic mutation in the OPN1LW gene can lead to a form of color blindness that affects a person's ability to detect red light. However, women have two copies of the X chromosome, and they have normal color vision if only one copy contains the mutation. Why do women who carry one copy of the mutated gene still have normal color vision?

Answer 1

Women who carry one copy of the mutated gene still have normal color vision because they have another copy, which is not mutated, in the other X chromosome that will be the dominant one. As a result, the women are carriers of the mutated gene but not color blind.

Explanation:

Colorblindness is a sex-linked mutation. A woman has two X chromosomes, while a man has one X chromosome and one Y chromosome. The mutated gene that causes color blindness is on the X chromosome, and it is OPN1LW. So if a woman has one mutated OPN1LW in one of her two X chromosomes, the OPN1LW gene in the other X chromosome will be the dominant one stopping the woman from being colorblind.

In the case of men, as they only have one X chromosome, if there is a mutation on the OPN1LW in the X chromosome, the men will be colorblind because there is no extra copy of the gene, as it is in women.