Some science Qs and my replies to them - Part 251 - colour blindness

Krishna: The answer is “Yes”.

There are various reasons for colour blindness. We will have to understand them to know how this happens in both genders.

Usually conditions like color blindness are passed from parents to their children on groups of genes called chromosomes.

Some of these, called X and Y chromosomes, determine if you are male or female at birth. Males have 1 X chromosome and 1 Y chromosome, and females have 2 X chromosomes. The genes that can give you red-green color blindness are passed down on the X chromosome.

Since it’s passed down on the X chromosome, red-green color blindness is more common in men. This is because:

• Males have only 1 X chromosome, from their mother. If that X chromosome has the gene for red-green color blindness (instead of a normal X chromosome), they will have red-green color blindness.
• Females have 2 X chromosomes, one from their mother and one from their father. To have red-green color blindness, both X chromosomes would need to have the gene for red-green color blindness.

According to the Colorblind Awareness organization, about 1 in 200 women worldwide are colorblind compared to 1 in 12 men (1).

Colour blindness testing pictures

Blue-yellow color blindness and complete color blindness are passed down on other chromosomes, so they affect males and females equally (2).

Blue-yellow color blindness is passed on via an autosomal dominance pattern that is not sex-linked. It can be passed to an offspring by either genetic parent. A single copy of the genetic change (in this case, OPN1SW) is enough to cause the disorder.

In the case of blue-yellow color vision, people have a 50/50 chance of inheriting the condition from a parent who has it. It can also happen due to a new gene mutation.

Achromatopsia is a severe form of colorblindness (3). People with achromatopsia can’t see any colors. Those with this condition only see black, white, and shades of grey in between. Unlike other forms of color vision deficiency, it can also cause vision issues such as light sensitivity, limited visual acuity, farsightedness, and nearsightedness.

It’s inherited via an autosomal recessive pattern. Both parents have to have the recessive gene to pass it down, which is why it’s so rare. There are also some cases of achromatopsia where the cause is unknown. Only 1 in 30,000 people worldwide have this condition

Color vision deficiency that isn’t caused by genes is called an acquired vision deficiency. Potential non-genetic causes of colour blindness include:

Color blindness can also happen if your eyes or the part of your brain that helps you see color gets damaged. This can be caused by ….

• Eye diseases, like glaucoma or macular degeneration
• Brain and nervous system diseases, like Alzheimer’s or multiple sclerosis
• Some medicines, like Plaquenil (a rheumatoid arthritis medicine)
• Eye or brain injuries
• Certain drugs
• Chemical exposure
• Eye disorders
• Damage to the optic nerve
• Damage to areas of the brain that are responsible for visual processing
• Diabetes, Glaucoma, Leukemia, Liver disease, Alcoholism, Parkinson's ,Sick cell anemia can also cause colour blindness.

Color vision can also diminish as you get older. In cases of non-genetic colorblindness, your eyes may be affected differently. Your color vision may also get worse as you get older, especially if you get a cataract .

These non-genetic factors can cause colour blindness in both males and females.

Footnotes:

1. Colour Blindness
2. Color vision deficiency: MedlinePlus Genetics
3. Achromatopsia: MedlinePlus Genetics