I know a high school teacher who teaches science and had just finished a unit on sight and genetics with her students. She asked me if I’d like to be interviewed by her ELL students in class one day. Before I came to class, she asked her students to think of some questions, and then they each selected one to ask me while I was there (she told them ahead of time that I was an artist, so they were really interested in that). The students were already familiar with Punnett squares so we did those on the whiteboard.
It was a really fun and interesting experience for all of us, so I kept a copy and wrote my answers for others who may be interested. (Student names are changed).
Josephina: Were you born color-blind?
Yes, I was born color-blind. Color-blindness is caused by a person’s genes, which they inherit from their parents before they are born. So there is no way for someone with typical color vision to later become color-blind later in their life.* There is also currently no way to cure color-blindness, so I will be color-blind my whole life.
However, being a woman who is color-blind is pretty rare: color-blindness affects about 1 in 20 males, but only 1 in 400 women. Color-blindness is a sex-linked trait, which means that the genes are on the sex chromosome X. Males and females are affected differently because males only have one X (XY), but females have two X’s (XX).
If a boy inherits an X with a defective color vision gene (X`), he is color-blind because he has only that copy of those genes. A girl can inherit an X with a defective gene, but she can still have normal color vision because the effective gene on her other X chromosome will compensate for the defective one. In order for a girl to be color-blind, she has to have two copies of the mutated gene (X`X`), which is why it’s so rare.
Jan: What colors can’t you see?
The term “color-blindness” is not completely accurate. I can see all the colors, but I do not see them as well as people with typical vision see colors, or I have trouble distinguishing between two similar colors. For example, purples might look like blue to me, or certain greens and browns may look the same.
Sometimes color-blindness is called “color vision deficiency” because the condition comes from a deficiency in one or more of the cones in the eye. There are three cones in the eye that different ranges of color, and my understanding is that the cones that are most sensitive to red colors is defective,
Berny: When did you learn you were color-blind?
I learned that I was color-blind at a very early age because my parents knew that there was a chance I could be color-blind. The eye doctor gave me the Ishihara test for color-blindness [of identifying numbers from an image composed of dots], and it indicated that I had a type of color-blindness called “red-green color-blind.”
My mother’s father (my grandfather) was color-blind, which means that my mom has one normal gene and one defective gene, and her genotype is XX`. She’s called a “carrier” because, although she herself is not color-blind, she can “carry” the color-blind gene to her children. My father is color-blind, so his genotype is X`Y. To find out the chances that I would be color-blind, we can use a Punnett square (shaded gray indicates a person who is color-blind):
The ratio of probability is 25% non-color-blind girl, 25% color-blind girl, 25% non color-blind boy, and 25% color-blind boy. Or in other words, regardless of whether I was born a boy or girl, there was a 50/50 chance that I would be color-blind.
Jorge: Do you have any siblings who are color-blind?
Yes, I have a twin sister, and she also happens to be color-blind. So, of all the people in my immediate family, my mom is the only one who is not color-blind. She thinks it’s funny when she has to settle an argument on the particular color of a car.
Mimi: How did you feel when you learned that you were color-blind?
Perhaps because I learned about my color-blindness at an early age, I was not upset because I just accepted it as part of who I was. There are some things I knew I could not do because of my color-blindness, such as becoming a commercial airplane pilot. But, my color-blindness also didn’t stop me from becoming an artist!
I’ve never had typical color vision, so I can’t compare how “my” world compares to the world other people see. But, if I’m missing out on anything, I can’t tell or it doesn’t really make a difference. Besides, being a color-blind woman is unique and I enjoy learning about it and talking to others about it.
Lucita: Do you think your kids will be color-blind? Why?
If I have kids, there is a chance they will be color-blind, but it depends on who their father is and whether he is color-blind or not. We can solve this problem using a Punnett square again.
So this is me, with the double color-blind chromosomes X’X’ and a color-blind man with X`Y.
All of our children would be color-blind! This is because they would only inherit X’s that have a mutation. Let’s look at another Punnett square for a father that had typical color vision (XY).
So, if I ever have a son, he will be color-blind: he would inherit the X` of his XY from me, and I could only give him X’s with a defective gene. If I had a daughter, she would be a carrier, because one of her X’s would be from me, and the other (normal) X would be from her father. She would have normal color vision.
Allie: Who helps you identify colors?
Everyone! When I create art, I will ask my coworkers to double check the colors I have used to make sure I have not accidentally make something that was supposed to be gold actually a yellow-green color, for instance.
My friends will help me notice certain flowers on a hike that I wouldn’t otherwise notice. Once we were in the woods and they were like, “Wow! Look at those beautiful orange flowers on that tree!” It was in the distance, and I couldn’t see it at all. But, after they were able to help me exactly which tree they were talking about, I could see the orange flowers that they had noticed immediately.
When I’m by myself, I will even ask strangers to double check colors for me in the store, to make sure I am buying blue sheets instead of purple sheets, for example.
Natelli: Is it hard to identify the colors of your clothes?
In the past, there have been times when I was convinced I had a pair of brown pants and they were actually a green color, and I didn’t find out until much later when I said something about “my brown pants” and my friends were confused and corrected me. (Laughs). Now that doesn’t happen so much anymore because I think colors that are easy for me to see are more appealing to me. I’ve wondered if this is related to my color-blindness–I wear a lot of blue because I think it is appealing and has a lot of variations. I also wear a lot of grays and blacks with some bright colors. But, my color-blind sister prefers to wear much different things than me, so it’s probably just personal preference.
Han: How do you draw a beautiful picture? What are problems that you have when you draw a picture?
I have trouble matching colors. One time when I was in high school, I was painting a picture of a cloth that was tan with brown stripes. I ran out of paint, and when I went back to mix more paint, I accidentally used a dull green-brown color instead of brown. My teacher caught my mistake, but I had to go back and correct the green parts to brown using the correct paints.
Bobbi: How long have you been driving? Is it difficult because you’re color-blind?
I have been driving since I was sixteen years old. There are certain challenges to driving as a color-blind person, but there are ways to compensate for it. For example, a light signal has green, yellow, and red colors, and sometimes it can be difficult to distinguish the yellow and red colors. However, I know that the green light is on the bottom and the red light is at the top, so I can distinguish those. Some countries have extra cues to help people with color-blindness, like having different shapes for each of the lights or adjusting the colors so they are more easily distinguished.
Alfredo: What other things are difficult to do because you’re color-blind?
This didn’t happen to me, but someone I know once had difficulty doing his job because he had to read text on a computer screen that had different colors instead of just black on white background. He was fired and one of the reasons they gave is that he was not able to learn to use the computer very well. Even though he had asked them to change the colors on the screen, and it was possible to do so, they had refused to change it. To make a long story short, he took his employer to court and the case was picked up as a discrimination case, because color-blindness is considered a mild “disability.” Eventually he won and was able to get compensated for lost wages.
Thank you for your questions, this was a lot of fun! I hope you were able to learn something from me.
– The Science Slug
*After doing additional research, it turns out that it is possible to acquire color-blindness later in life: http://www.colourblindawareness.org/colour-blindness/acquired-colour-vision-defects/
References and links used in this post
- Punnett square: http://en.wikipedia.org/wiki/Punnett_square
- Ishihara plate image: http://en.wikipedia.org/wiki/Ishihara_colourblindness_test#mediaviewer/File:Ishihara_11.PNG