Sex-Linked Inheritance & Colour Blindness — NEET Biology
✅ Asked in NEET 2024Colour Blindness: It is a sex-linked recessive disorder due to defect in either red or green cone of eye resulting in failure to discriminate between red and green colour. This defect is due to mutation in certain genes present in the X chromosome. It occurs in about 8 per cent of males and only about 0.4 per cent of females. This is because the genes that lead to red-green colour blindness are on the X chromosome. Males have only one X chromosome and females have two. The son of a woman who carries
NTA focuses on why colour blindness appears more frequently in males than females due to X-linked recessive inheritance. The key concept is that males (XY) have only one X chromosome, so a single recessive allele expresses the phenotype, while females (XX) need two copies to be affected. Students often confuse whether a carrier mother's sons have 50% or 100% chance of being colour blind—the answer is 50% (they inherit either the normal or defective X). Remember: sons inherit X from mother only, so carrier mother (XAXa) × normal father gives 50% colour blind sons. This pattern appears repeatedly because understanding X-linked inheritance is fundamental to Mendelian genetics.
This paragraph was tested 3 times in NEET.
A carrier female for colour blindness marries a normal male. What is the chance that their son will be colour blind? (NEET 2024)
A woman has an X-linked condition on one of her X chromosomes. This chromosome can be inherited by: (NEET 2018)
If a colour-blind man marries a woman who is homozygous for normal colour vision, probability of their son being colour-blind is: (NEET 2016)
Through deep analysis of NEET and NTA, 88 of 90 questions from the NEET 2026 paper were matched straight from the MedicNEET Biology question bank.
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