The Truth about Colour Blindness – Gaijinhan

The Truth about Colour Blindness

Come this April, I would’ve spent 31 years of my life with colour blind deficiency (beating around the bush to hint at my birthday). Of course, since it is not curable, I’ll probably spend the rest of my life this way unless someone figures out some way to correct my defective chromosome.

I’ve been ridiculed by people who find it funny making a joke of my inability to distinguish certain colours and I’ve also been asked by people who find it the most incredulous thing to imagine the world I see.

For the curious, this is not what I see

This is probably closer to what I see.

Since the probability of men having colour blindness is much higher than women, many people seem to assume that men with colour blindness pass it on to their children, which is incorrect. Or not totally correct.

Here’s to explain it in simple terms:

Men’s chromosomes are X-Y while women’s chromosomes are X-X.

Colour blindness occurs when the X chromosome is faulty. Since men only have one X chromosome, they get colour blindness if that sole X chromosome is faulty. Women are less likely to get colour blindness because they have two X chromosomes, and as long as one of them is not faulty, they will have normal colour vision.


* Red X = faulty X chromosome

When a couple gets married and gives birth to their offspring, their children will inherit their chromosomes. Let’s use the above couple to better explain what could happen.

Since the boy will also have X-Y chromosome, and only the father has a Y chromosome, the boy must inherit the Y chromosome from the father. His X chromosome will then naturally be inherited from the mother. If it happens that the mother passes on her faulty X chromosome to the child, then the boy will be colour blind as below.

Of course, there is also the possibility that the mother passes on the healthy X chromosome to her child. In which case, the boy will have normal colour vision. In any case, the father has no role in playing a part in the boy’s colour vision.

For girls, since they have X-X chromosomes, if the father is colour blind, he will definitely pass on his faulty X chromosome to the daughter. But as long as the mother passes on her healthy X chromosome to the girl, she will have normal colour vision as below.

Of course, there is also the possibility that the mother passes on the faulty X chromosome to the girl. In which case, she will be colour blind.

Thus, the reason for the low probability of girls having colour blindness is because 1) the father must be colour blind for the daughter to have any chance of being colour blind and 2) the mother must have at least one faulty X chromosome.

Now that you have one confusion cleared up, let’s create one more for you: I have absolutely no problems distinguishing traffic light colours.

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