Why is colour blindness less common in women?

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An explanation of why colour blindness is more common in males, and its effects on female heterozygotes.

Question

Why is colour blindness less common in women?

Answer

Colour blindness is less common in women primarily due to its genetic basis. The most common form, red-green colour blindness, is an X-linked recessive disorder. This means the gene responsible for this condition is located on the X chromosome. Since men have only one X chromosome, a single recessive gene on that chromosome will result in colour blindness. Women, however, have two X chromosomes, so a recessive gene on one can be compensated by a normal gene on the other, making them less likely to be affected and more likely to be carriers instead.

Genetic Basis

X-Linked Recessive Inheritance: Colour blindness is often inherited in an X-linked recessive pattern, which explains its higher prevalence in males (who have one X chromosome) compared to females (who have two X chromosomes) (Alkhalaf and Al-Khafaji, 2022; Singh and Sharma, 2021; Lawson et al., 2024; Henry et al., 2020).

Prevalence

Higher in Males: Studies consistently show a higher prevalence of colour blindness in males compared to females. For instance, prevalence rates are around 8% in males and 0.5% in females (Singh and Sharma, 2021; Lawson et al., 2024; Henry et al., 2020).
Specific Studies: In various studies, the prevalence of colour blindness in males ranged from 3.6% to 4.87%, while in females, it was significantly lower, ranging from 0.4% to 0.64% (Alkhalaf and Al-Khafaji, 2022; Saha et al., 2021; Singh and Sharma, 2021).

Types of Colour Blindness

Red-Green Deficiency: The most common type of colour blindness is red-green deficiency, which includes protanomaly and deuteranomaly. These are more prevalent in males due to the X-linked inheritance pattern (Alkhalaf and Al-Khafaji, 2022; Saha et al., 2021; Henry et al., 2020).

The lower incidence of colour blindness in women is primarily due to the X-linked recessive inheritance pattern of the condition. Women are less likely to be affected because they have two X chromosomes, allowing a normal gene on one to compensate for a defective gene on the other. This genetic mechanism results in a significantly higher prevalence of colour blindness in males compared to females.

References

Alkhalaf, A., & Al-Khafaji, R., 2022. Prevalence And Allele Frequency Of Colour Blindness In Al-Najaf Al Ashraf Province. Medical Science Journal for Advance Research. https://doi.org/10.46966/msjar.v3i2.43

Saha, R., Sarkar, I., Chatterjee, T., Samaddar, S., & Sen, S., 2021. A Hospital-Based Cross-Sectional Study to Estimate the Prevalence and Sex Distribution of Colour Vision Deficiency among School Going Children Attending a Tertiary Eye Care Centre in Kolkata City, West Bengal, India. Journal of Evidence Based Medicine and Healthcare. https://doi.org/10.18410/jebmh/2021/541

Singh, A., & Sharma, V., 2021. Commentary: Significance of early screening for colour vision in children. Indian Journal of Ophthalmology, 69, pp. 2026 – 2026. https://doi.org/10.4103/ijo.IJO_648_21

Lawson, E., Khan, A., Wessels, Q., & Taylor, A., 2024. Congenital colour vision deficiency in healthcare professionals: a scoping review protocol of the impact on clinical practice and patient safety. BMJ Open, 15. https://doi.org/10.37766/inplasy2024.11.0099

Henry, N., Stephenson, C., Clough, R., & Shea, S., 2020. Addressing and Overcoming Difficulties for Students with Colour Vision Differences or Deficits (Colour Blindness) in Educational Instruction and Assessment. The FASEB Journal, 34. https://doi.org/10.1096/fasebj.2020.34.s1.00350

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