Wednesday, September 09, 2015

Colour Blindness: The Science, Simplified

This is the second post in my series on parenting a colour-blind child (the first is here).  This series was born when I discovered that googling "colour blind children" and other combinations of those words, leads to a lot of articles and blogs about teaching children to ignore race.  Which is ridiculous in and of itself, and also ridiculous because there is a Real Thing called Colour Blindness that Real People deal with daily. While there are some excellent resources out there, they are few and far between.  So I decided to use my resources and share a bit of my research and experiences on this blog.  I will be writing a series of posts on the topic over the next little while and will update with further posts when I have more to share.  If you are also parenting a colour-deficient child, are colour blind yourself, are a teacher (because, whether you know it or not, you've taught and will teach colour -blind students), or know people who fit any of these criteria, please feel free to read, share and comment.  I don't think enough of us are talking.

This post is, as promised, some of The Science behind colour deficiencies like my son's.  I'll keep it simple because, well, I'm not a scientist. . . and I also think that simple explanations are easier for all of us.


There's More Than One Type of Colour Blindness:

There are three, actually:  protanopia (red-green and blue-green), deuteranopia (red-green; most common) and tritanopia (blue-yellow).  And not everyone who has one suffers to the same degree - it is possible to be only a little bit colour deficient.  How? Because of the way colour blindness (or deficiency) works.

How Does Colour Blindness Work?

Glad you asked :) In human beings, our eyes see using rods and cones to detect light and colour.  Rods can not detect colour - only cones can.  There are three different types of cones in the human eye which detect red, green and blue.  In a colour-deficient person, they may have fewer cones (or faulty cones) of one (or more) type and consequently have difficulty perceiving that colour.  Cones are more sensitive when there is a lot of light.  This is why it is easier for everyone (but particularly a colour-deficient person) to see colour when it's light versus when it's dark.

Since the cause of colour deficiencies seems to be a flaw or deficiency in the cones of the eye, it is not something that will change with time. If your colour blindness is genetic, the way you see and perceive colour will stay the same for your whole life.  Extra time on tests will never aid a child in determining one colour from the next and a child who experiences difficulties with colour for this reason will not grow out of it by high school.  The only thing that can change is the strategies the colour deficient learn to use, the supports they receive and their attitude toward school and colour-related tasks (based partially on the support and attitudes of educators, in my opinion).

How Does Someone "Get" Colour Blindness?

Most cases of colour blindness are genetic.  That means that it's not something that you can just "get" - it's something you're either born with or you're not.  Let's refresh ourselves on how the sex of a child is determined (relax - I'm not talking about how that child is created here):



Every female has two X chromosomes, while males have an X and a Y chromosome.  When a child is created, each parent provides one of these sex chromosomes.  Since mom only has X chromosomes, that's what she gives.  If the child is female, dad provided an X chromosome; if the child is male, dad provided a Y chromosome.





The gene that causes red-green colour blindness is coded on the X chromosome.  Not every X chromosome has this gene but some do.  If you are female, both of your X chromosomes would need to have this genetic code in order for you to be colour blind (that's why it's more rare among women than men).  If you are male, however, it only takes one, since you only have one.  Make sense?

So here's how colour blindness can be passed along in a family:



This is my family:  my mom has no genes for colour blindness but my father is, himself, red-green colour blind.  I don't have any brothers but you can see that if I did, the fact of my dad's colour blindness would have no effect on them (he passes along his Y chromosome to male offspring which is irrelevant in a discussion of colour deficiency).  You can also see, however, that both my sister and I inherited a "normal" X chromosome from my mother and a "colour blind" X chromosome from my father.  That makes us "carriers" of the gene; we are not colour blind, ourselves, but have the chance to pass that gene onto our offspring.




And here's my own family in which I am "mom" (below).  See me there with one "normal" X chromosome and one "colour blind" version? I am a carrier.  My husband has normal colour vision.  If we had daughters, they would either be carriers like me (if I gave them the "colour blind" chromosome) or have no genes for colour deficiency at all.  But I didn't have daughters.  My sons have inherited no genetic material for colour blindness from their father, because they are boys.  From me, they either inherit the "colour blind" chromosome or the "normal" one - a 50-50 chance.  Since my older son is colour deficient, he has inherited the "colour blind" one.  We won't know which one my younger son inherited until he is older.



















But what if I had married a colour-blind man?

My daughters (if I had any) would have a 50% chance of being colour blind, otherwise they would be carriers.  My sons would have the same potential outcomes as above.

Just in case you're interested (or it applies to you), here are the potential outcomes for a colour-blind mother with both a colour-blind and non-colour-blind partner:

If the father has normal colour vision, a colour-blind mother will have either a carrier daughter or a colour blind son.  But if you are lucky enough to hit the genetic lottery and have two colour-blind parents, you will likely be colour blind, regardless of sex.

The Gist:

Colour blindness is usually genetic.  That means you can't change it and you can't prevent it.  Someone either has normal colour vision or they do not.  Not all colour blindness is equal:  some people have difficulty with different colours than others; some have more severe deficiencies than others.

As parents (our children's first teachers) and educators, we should know this.  A child cannot "get over" their colour blindness any more than a child who uses a wheelchair can "get over" not being able to walk.  Just as we would never expect that child to get up and achieve in Physical Education the same way as a child who does not use a wheelchair, we should acknowledge that our colour-blind children and students will have some tasks that will prove much more difficult for them.  While we can teach these children some strategies which will (hopefully) allow them to achieve, that will not erase the challenge.

Even though there are some key genetic requirements needed for a child to be colour blind, it is not actually as rare as one might think.  8% of all males have some form of colour blindness (fewer women but they do exist).  That means there is likely someone with a colour deficiency in every classroom, whether we know it or not (whether they know it or not!).  You have likely met many colour-blind people in your lifetime and will meet many more!

Previous:  Colour Blindness:  Figuring It Out                Next:  Colour Blindness:  Famous Faces

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