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.

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.


18 Responses to “The Biology behind Red-Green Color Blindness”

  1. bornfool Says:
    March 8th, 2006 at 1:12

    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: http://lamonalicious.blogspot.com/

    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 Says:
    March 8th, 2006 at 11:01

    bornfool,

    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. Lusidvicel Says:
    December 18th, 2006 at 17:50

    Hello, i love http://www.colblindor.com! Let me in, please :)

  4. mike Says:
    June 2nd, 2007 at 14:47

    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?

  5. Daniel Flueck Says:
    June 2nd, 2007 at 15:35

    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.

  6. genetica discromatopsiei « Sunt discromat ?i vreau ?ofer Says:
    July 12th, 2007 at 10:41

    [...] Daniel Flueck – The Biology behind Red-Green Color Blindness [...]

  7. vanessa Says:
    February 7th, 2008 at 12:47

    I belong to the very few women affected. That made it impossible for my father to pretend I wasn’t his daughter;-))

  8. Acushla » Blog Archive » COLOR BLINDNESS, GLASSES, AND CHILDHOOD TICS… Says:
    August 30th, 2008 at 1:44

    [...] shocking news.  Although Brandon’s vision tested at 20/20, he is apparently red-green colorblind.  They did the Ishihara test on him via a book that he was to look through and say the numbers, [...]

  9. ED Says:
    October 13th, 2008 at 10:28

    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….

  10. Leonora Says:
    November 2nd, 2008 at 22:27

    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?

  11. Daniel Flück Says:
    November 14th, 2008 at 22:34

    Leonora, an interesting question which I tried to answer in the article If a Women is a Carrier of Color Blindness does she also Suffer from it?.

  12. Leonora Says:
    November 17th, 2008 at 23:25

    Hi Daniel, thanks for your fascinating explanation. I’ve written a comment in the other thread.

  13. danielle Says:
    March 17th, 2009 at 14:02

    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.

  14. Daniel Flück Says:
    March 17th, 2009 at 21:02

    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.

  15. .colblindor « fin. Says:
    September 17th, 2009 at 9:14

    [...] #03 Color blindness is more prevalent among males than females, because the most common form of color vision deficiency is encoded on the X sex chromosome. [...]

  16. Anton Says:
    December 25th, 2009 at 20:53

    Thank you, it was interesting. Have more to these posts.

  17. jesse Says:
    January 10th, 2010 at 17:19

    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?

  18. sohbet Says:
    February 24th, 2010 at 22:37

    “added feature” to my color vision? or am I finding ghosts in dark rooms?

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