Color blindness, or color vision deficiency, is more common in males. This is due to how parents pass down a chromosome associated with the male sex.

Red-green color vision deficiency is the most common type of color blindness. Someone with this type finds it difficult to differentiate between red and green.

The probability of having red-green color vision deficiency is linked to the X chromosome, which males inherit from their mother, and females from both parents.

This article looks at color blindness and sex, the role of genetics, and color blindness types and statistics.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Color vision deficiency refers to an inability to perceive certain colors clearly. Different types of color blindness can make it hard for a person to tell the difference between specific color combinations.

The most common type is red-green color vision deficiency. People with this type of color blindness can have difficulty differentiating between green and red.

Red-green color blindness is more common in males than females. Around 8% of males and 0.5% of females worldwide have this type.

The much higher prevalence in males is due to genetics and how certain variant genes pass from parents to children within chromosomes.

Other types of color blindness do not involve sex-related chromosomes and are equally prevalent in males and females.

There are several potential causes of color vision deficiency, including injuries, diseases, and certain medications.

However, genetics is most often the cause of the most common types of color vision deficiencies.

Parents pass down red-green color vision deficiency, the most common type, through variant genes in the X chromosome.

Chromosomes are structures that carry genetic information. The X chromosome carries genes that influence a person’s sex at birth. They can also carry variant copies of the OPN1MW or OPN1LW genes that cause red-green color blindness.

The genes carry instructions for creating a protein the eye requires for clear color vision. Variations in these genes can prevent the body from correctly assembling these proteins.

Males inherit one X chromosome from their mother, while females inherit two X chromosomes, one from each parent.

For a male to inherit red-green color blindness, the single X chromosome they inherit must contain a variant of the OPN1MW or OPN1LW gene. However, for a female to inherit red-green color blindness, both X chromosomes would need to contain the variant gene.

It is rarer for a female to inherit two X chromosomes containing the affected genes than for males to inherit only one. This means there is a higher probability of red-green color blindness affecting males.

Cone cells are a type of nerve cell in the retina that detect either red, green, or blue light wavelengths. Color blindness occurs when cones do not function as usual.

Light stimulates the cones as it enters the eye, causing the cells to communicate signals to the brain through the optic nerve. The brain uses the information from the cells to determine a person’s perception of color.

When one or more of the cone cells do not function correctly, different types of color blindness can occur.

Types of color vision deficiency include:

  • Red-green: This is the most common type. Subtypes include deuteranomaly, which causes people to perceive some shades of green as red, and protanomaly, which makes red appear green. A person may also have a combination of the two subtypes, which may completely prevent them from being able to differentiate between red and green.
  • Blue-yellow: A person with this type may have difficulty differentiating between various color combinations. Subtypes include tritanomaly, which affects the ability to distinguish between blue and green and between yellow and red. Tritanopia is another subtype that can make it difficult for a person to tell the difference between pink and yellow, green and blue, and red and purple.
  • Complete: This is a rare type of color vision deficiency, which people also call achromatopsia or monochromacy. Someone with this type cannot see colors at all.

Statistics

  • Color blindness is more common in white people.
  • Red-green color deficiency is the most common form, occurring in about 1 in 12 males and 1 in 200 females with Northern European ancestry.
  • Blue-yellow color vision deficiency is rarer and affects both males and females equally. This subtype presents in less than 1 in 10,000 people worldwide.
  • Complete color blindness only affects around 1 in 30,000 people.
  • One study found that 25% of people with anomalous trichromacy, in which one type of cone does not function correctly, were unaware that they had color vision deficiency.

Is color blindness dominant or recessive?

The most common type of color blindness, red-green color vision deficiency, is X-linked recessive.

This means the condition can occur in males who inherit one copy of the variant gene but can only occur in females who inherit two copies of the variant gene.

How is color blindness inherited?

A person inherits color blindness when a parent passes down variant genes in specific chromosomes.

Color blindness is more common in males due to the way inherited chromosomes and genes behave.

Males inherit a single X chromosome from their mother, while females inherit an X chromosome from each parent.

X chromosomes contain genes associated with sex. They may contain variant genes that cause red-green color blindness. This is the most common type of color blindness.

Red-green color blindness can occur in males who inherit the variant gene within a single X chromosome. Color blindness can only occur in females who inherit variant genes in both X chromosomes, which occurs more rarely.