The most common inherited form of color blindness (red-green) is caused by a common X-linked recessive gene.
Mothers have an X-X pairing of chromosomes carrying genetic material, and fathers have an X-Y pairing of chromosomes. A mother and father each contribute chromosomes that determine the sex of their baby. When X chromosomes pair with another X, you are female. And when the X pairs with the Y, you are male.
If you have a common form of color blindness caused by an X-linked recessive gene, your mother must be a carrier of the gene or be color deficient herself.
Fathers with this inherited form of red-green color blindness pass the X-linked gene to their daughters but not to their sons, because a son cannot receive X-linked genetic material from his father.
A daughter who inherits the color-deficient gene from her father will be only a carrier unless her mother also has the color-deficient gene. If a daughter inherits the X-linked trait from both her father and her mother, then she will be color blind as well as a carrier.
Any time a mother passes along this X-linked trait to her son, he will inherit the color vision deficiency and have trouble distinguishing reds and greens. Again, a daughter can be a carrier but will have this form of color blindness herself only when both her father and mother pass along the X-linked gene. This is why more men than women are color blind.
