Both me and my Dad are colour blind. I know that my mom has to carry the gene for me to become colour blind. I’ve heard that colour blindness in women is rare, my eye doctor didn’t even want test me. But I don’t believe I am a specific type of colour blindness. I have trouble with any colour if it isn’t a true what they say “green” or “blue” or any other colour for that matter, if its next to another colour (ex. yellow next to green) How often does CB occur in women? And is there other types other then the “red/green” deficiency and being totally CB?
Here’s what I read.
Color Blindness is carried on the X chromosome.
Men only have 1 so if you have it your CB.
Women have 2 X chromosomes. to be CB, you have to have the CB gene on both… meaning, that to have a cB girl, both parents have to be carriers. Dad would be CD. mom would either be CB or carry.
Ishihara Color Blindness Test. Note that results may not be accurate, depending on the faithfulness of your video card/monitor combination to replicate colors.
Yes, I get the stares of disbelief, the doubting, the questioning, the sputtering “but - but -but women aren’t colorblind!!!”
Yes, some of us are. The figure I see is usually 1/2 of 1% That’s about 1,500,000 in the USA alone, about 40,000,000 world wide. A small percentage, but a lot in actual numbers.
Most are never diagnosed as colorblind. In part, this is because so many people are so sure that women are never colorblind the gals are never tested.
There are several types of colorblindness, many more than I have time to list right now. The most common is red/green, but there’s blue/yellow, and several others. Some types are not sex-linked, such as achromotopsia and occur with equal frequency in both sexes. In other cases, because of the genetics involved with sex-linked characteristics, women may be affected enough to be detected with an Ishihara test, but not enough to make a real difference in almost any activity.
If you want more explanation either someone else will be along or I’ll be back when I’ve got more time.
This isn’t quite correct.
Red-green colorblindness comes in two forms, called protanopia and deuteranopia. In protanopia, the gene for the red, or L, receptor, is damaged or missing. In deuteranopia, the gene for the green, or M, receptor is damaged or missing. These genes are located adjacent to one another on the X chromosome. A man who inherits one of these genes will have the corresponding form of red-green colorblindness.
However, because of what is called “X chromosome deactivation” (a process by which one of the woman’s X chromosomes is deactivated on a cell-by-cell basis), a woman who carries one but not both of the genes for protanopia or deuteranopia can actually be anywhere from totally colorblind to not colorblind at all, or even colorblind in one eye but not the other, depending solely on which X chromosome is deactivated in which regions of each eye. The usual result is a partial reduction in color vision resulting from a significant proportion of the L (protanopia) or M (deuteranopia) cones being defective or absent. The impairment can run anywhere from trivial (only showing up on color blindness tests) to complete.
A woman can be red-green colorblind without inheriting the defective gene from both parents. All it takes is one parent having the gene, either mother or father, and if the mother has the gene, she may not show any sign of it. (Of course, the gene can also arise spontaneously through mutation.)
Even more confusing is what happens when a woman inherits one, but not both, genes for either protanomaly or deuteranomaly. In protanomaly, the red (L) receptor gets its genes garbled with those for the green (M) receptor, resulting in the red receptor being replaced by one that is closer to being a yellow receptor. In deuteranomaly, the same thing happens to the green receptor. Males with protanomaly or deuteranomaly have impaired color vision, but not to the extent that a protanope or deuteranope would. (A deuteranomalous male might not have any discernable impairment except for the inability to pass color blindness tests.) However, a woman who has one but not both of the genes for either of these conditions may develop, depending on her X chromosome deactivation pattern, tetrachromaticity, or four-color vision. Her eyes will have, in addition to the usual red, green, and blue cones, a fourth cone with a peak response in the yellow range, giving her a greater capability to distinguish colors, including the ability to distinguish colors that most people cannot tell apart.
Tritanopia, the absence of the blue receptor, is not sex-linked (and is extremely rare), as is achromatopsia.
Another colorblind female checking in. Thought it’s mld enough that it only really shows up on the colorblindness tests. And one time when I found out a pair of corduroy pants were actually a dark maroon rather than brown.
Minor addition to KellyM’s post – the “red” and “green” cones’ peak spectral response are at approximately 560 and 530 nm, respectively. So they already are pretty close to each other in their response to a given wavelength:
http://www.unm.edu/~toolson/human_cone_response.htm
The “red” cone actually looks yellow, and the “green” cone looks yellowish green. Also, there are slight deviations in people’s actual cone pigments, even between individuals who aren’t colorblind, so YMMV.
An interesting story: My husband is an optician, and the optometerist at his shop discovered that a young girl who he tested was colorblind. “It’s very rare,” he told her mother. “Her father must be colorblind.”
“No, he isn’t,” she said, somewhat tensely.
The optometerist tried to explain. “He must be, genetically–”
“No, he isn’t.” she said, staring down the doc.
I’m guessing that her husband isn’t colorblind . . .
Podkayne, even if her husband is the father of the child, he doesn’t have to be colorblind for his daughter to be colorblind. Read my previous post for why.
Podkayne meant to say that the mother was color-blind, hence knew that her daughter got it from her. Whether the husband was the biological father is immaterial.
Actually, if the little girl is colorblind there is no requirement that her mother be also - just a carrier of the trait.
Now, as to what was really going on there, there are several choices.
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The woman’s husband is not the girl’s biological father, which has sort of been danced around a bit. Now, it may be that the daughter was conceived by sperm donation and the mother doesn’t want anyone to know that. Or maybe she cheated on her husband and certainly doesn’t want anyone to know that (which has also been implied). Or maybe she was divorced/widowed extremely early in the child’s life and remarried, but the girl thinks her daddy is her biological daddy and mommy either doesn’t want her to know or doesn’t want to explain it yet. Or maybe the little girl is adopted and the parents don’t want her to know/haven’t told her yet. Or it might be one of those dreadful “switched-at-birth” cases. In other words, even if the husband isn’t the biological father there may be no foul play whatsoever, but that doesn’t mean the family wants the facts trumpeted to the four winds.
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As has been mentioned, the mutation can spontaneously arise, in which case the little girl may, in fact, be the biological child of her parents but also be colorblind.
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Wandering into the territory of the extremely rare, if the father has one of two chromosome abnormalities the girl could be biologically his daughter, inherit the colorblind gene from him, and yet he could be unaffected. The first instance is if he is an XXY male. Although they are usually sterile they aren’t always, and certainly they aren’t always detected at birth so even he may not be aware of the condition. Just as in women, in an XXY male in evey cell one of the two X’s is randomly chosen for suppression, so the colorblindness effects follow the female pattern as explained by KellyM. In which case the man could pass on the colorblind trait without being affected by it himself. The other instance involves chromosomal “mosaicism”. If two fertilized eggs merge early enough in development you wind up with one individual with two different genetic signatures. Some cells have one set of genes, some the other. So the cells making up the eyes could have normal color visiion genes, and yet the cells that generate the sperm to make the girl child might have had the colorblind trait. Although both of the above are rare, they are possibilities. The most interesting story I heard about the mosaicism effect involved a paternity test where the father was found to be the father alright - but the mother wasn’t the mother, despite giving birth to the child. Which is ridiculous, of course. Turns out the DNA making the woman’s blood wasn’t the same set of genes used by her reproductive organs.
So what this comes down to is that folks who, in the course of their work, discover these little anamolies, should probably keep their mouths shut about some of the possible implications of their discovery, because the odds are they don’t know for sure what is really going on, and probably it’s best they don’t get involved.
This page gives a nice comparison of what normal people see, vs. what totally colour blind or red-green colour blind people would see (not the hidden numbers in dots test… rather a normal everyday image) :