Can Women Be Color Blind?

Why it's rarer in women

Red-green colour blindness is X-linked and recessive. Women have two X chromosomes; men have one. For a woman to be red-green colour blind, both of her X chromosomes must carry the affected gene. For a man, a single affected X is enough, because he has no second copy to compensate. Needing two affected copies instead of one is exactly why the female rate is so much lower.

How a woman becomes color blind

A woman is red-green colour blind when she inherits an affected X from both parents, typically a colour-blind (or carrier) mother and a colour-blind father. This is uncommon, but far from impossible, especially where colour blindness runs in both families.

Carriers: normal vision, but they pass it on

Most women who "have colour blindness in the family" are carriers: one affected X and one typical X. They usually see colour normally, but each of their sons has a 50% chance of being colour blind, and each daughter a 50% chance of being a carrier. This is how the trait travels through generations, see the genetics of colour blindness.

Blue-yellow is different

Blue-yellow (tritan) deficiency isn't carried on the X chromosome, so it affects women and men about equally, though it's rare overall. Acquired colour vision changes (from ageing, medication or eye conditions) also affect both sexes; read about causes.

Could you be a carrier, or colour blind?

Many women only discover a mild deficiency, or that they're a carrier, when a child is diagnosed or they take a test out of curiosity. If colour blindness runs in your family, it's worth a quick check. Take the free color blind test to screen your own colour vision, and consider a professional exam if it matters for work or family planning.