The Biology behind Red-Green Color Blindness

Red-green color blindness is in the majority of cases provoked through a defective X-chromosome. Human beings have 23 different pairs of chromosomes whereof one pair is the so called sex-chromosome. This pair consists of two X-chromosomes on women and one X- coupled with one Y-chromosome on men. Color vision in the red-green area is coded on the X-chromosome which is called a sex linked trait.

This concludes if a man is a carrier of a defective X-chromosome he will suffer from color blindness. On women the not defective chromosome is in charge and therefore she is not colorblind but a carrier for color blindness. Because a women needs two defective X-chromosome to be affected this symptome is called X-linked recessive. A very interesting conclusion of this: If you are male and your father suffers from a red-green color vision deficiency you can not inherit it from him. Only women can be carriers for color blindness who pass it on to their sons.

Let’s have a look at some illustrations. On the left you can see how the disorder is passed on from an affected father to his children. The sons are unaffected and do not have the mutation. The daughters are not affected but are both carriers of the disorder because they inherited the defective X-chromosome from their father. The illustration on the right side shows a mother which is a carrier and a father which is unaffected. Their son is at a rate of 50% affected i.e. red-green colorblind and their daughter is at the same rate either are carrier or unaffected.

X link Recessive Mother And Father

In the last illustration we coupled an affected man with a women which is a carrier. As you can see their children are at a rate of 50% affected. This is the only case shown here, where a women can be affected i.e. suffering from a red-green color blindness. If the children are unaffected the daughter is anyway a carrier of the disorder. The not shown combinations where man and women are either both affected or both unaffected are left to the reader…

I hope this could give a better insight into the biology behind color blindness. It has to be noted that these remarks are only true for red-green color blindness. Blue-yellow color blindness (tritanopia) is linked to the chromosome pair 7 and therefore sex independent. Further readings on this topic and more details can be found under the following links:

The above illustrations are provided by the U.S. National Library of Medicine, 7th March 2006.

24 responses on “The Biology behind Red-Green Color Blindness

  1. bornfool

    A couple of posts ago on my blog you asked me if I had the url’s of the blogs I quit reading because of my color-blindness. I don’t have them but I just ran across a couple that are extremely difficult for me to read. One of them is this:

    I can read this one but it’s very difficult. It’s not like the one’s I ran across that were invisible to me, but this one is more trouble than it is worth.

    Sorry, I just went back to look for the other and I already lost it.

    I’m red/green color blind like you. You explain it quite well on here. I get asked all the time, “If you’re color blind, what color is this?” I try to explain it to them, but I don’t do a very good job.

    Thanks for stopping by.

  2. Daniel Post author


    thanks for stopping by and making investigations to answer my question. I had a look at the blogsite you posted: the titles are what bothers me most. They are popping out, making me almost dizzy.

    I hope with my blog people can get a better understanding of colorblindness and can answer the question “what color is this?” by themselfs.

  3. mike

    i red/green color blindness. i have question. my father is red/green color blindness but my mother is not. according to the chart i should not have it but why am i a red/green blindness?

  4. Daniel Flueck Post author

    Mike: you didn’t inherit the color blindness from your father, that’s for sure. But your mother can be a carrier and maybe the father of your mother is colorblind? It’s often passed on from grandfathers to their grandson.

  5. ED

    My mom is color blind and so all of her sisters, all of her sisters boys and girls are color blind… BUT i am not color blind… i smell sumthing fishy….

  6. Leonora

    Here’s a question for experts: according to a vision test in a magazine she did recently, my mother has a slight red-green weakness, which, however, is hardly noticable in daily life. Is this also ‘colour blindness’, although that is really rare in women, and it’s nothing compared to her father’s colour blindness, which was pretty severe? Or can it be due to her being a carrier?

  7. danielle

    I am also colorblind. (color dumb if you ask my grandfather. My father and my grandfather on my mom’s side are colorblind. What are the chances of any of my kids being colorblind? My husband and his family are not.

  8. Daniel Flück Post author

    Danielle, I suppose you’re talking about red-green color blindness. In this case both of your X chromosomes are colorblind. This results in: all your boys will be colorblind and all your girls will not be colorblind (because your husband isn’t). That’s at least what the genetic inheritance patterns tells us.

  9. jesse

    I discover that I have red-green color blindness, but in fact I have perfect color vision as well. I have taken tests where I pass all colors but I can see double images in the pictures used for red-green color blindness tests. Is it possible that this can be an “added feature” to my color vision? or am I finding ghosts in dark rooms?

  10. Em1975

    OK, I’m hoping a question can be answered for me. My youngest daughter – 3 1/2 years old – appears to be red/green color blind. We have thought this for about a year and a half – she knows ALL of her colors (even lights & darks now) but gets red or green wrong about half the time (so, if something is red there’s a 50/50 chance she will say red or green). This morning she seemed to confirm that she might be red/green color blind when she said to me, “Mom, red and green are the same color, right?” Here’s my question…
    According to this description of genetics, the only way she could be affected would be if I were a carrier and my husband was affected. I don’t know of anyone in my family who is color blind, but regardless of that, my husband is NOT color blind. How could this be?? Any explanations would be really appreciated!

  11. Daniel Flück Post author

    Em, just some thoughts about your daughter:
    – this is still a very young age to tell if someone is colorblind or not,
    – different severity occur, so maybe there is someone colorblind you don’t know about,
    – color blindness can be inherited down through many generations,
    – genetics is not always a straight calculation. There are many other factors who can influence it.
    So, please be patient – and don’t worry.
    – Daniel

  12. Myrtonos

    Here is a question, what if a red-green colorblind man conveives children with a blue-yellow colorblind woman?

  13. Daniel Flück Post author

    Myrtonos, nice question. None of them will be colorblind. – But this is only working in an ideal world. So we actually don’t really know. – And the genetics I leave to you.

  14. Myrtonos

    But there are surely cases of this happeing. You say none of them will be colorblind but I wonder if in fact it might result in better than average color vision.

  15. Myrtonos

    Okay, what if say a red weak or green week man coceives children with a blue weak woman?
    I know that if say a green weak man such as Mr. Tomoiag? were to conceive children with the daugther of a red weak man, their daugters could very well have both normal and anomoulous red cones and thus see *more* colours than normal.