Identify the statements that are incorrect regarding colour blindness:
A. It is a sex-linked recessive disorder.
B. Individuals with the condition cannot differentiate between red and green colours.
C. It affects approximately 8% of females and 0.4% of males.
D. The disorder is caused by a mutation in genes located on the "Y" chromosome.
Select the correct answer from the options below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C and D
Colour blindness is a Mendelian disorder. The person cannot tell red from green because of a defect in the red or green cone of the eye. The genes for it lie on the X chromosome, and males have only one X. So the disorder is much more common in males than in females.
Statement A: It is a sex-linked recessive disorder. — True. The faulty gene is recessive and lies on a sex chromosome, so it is a sex-linked recessive disorder.
Statement B: Individuals with the condition cannot differentiate between red and green colours. — True. A defect in the red or green cone causes failure to tell red from green.
Statement C: It affects approximately 8% of females and 0.4% of males. — False. The figures are reversed. It occurs in about 8 per cent of males and only about 0.4 per cent of females. A male needs only one faulty X to show it; a female needs two.
Statement D: The disorder is caused by a mutation in genes located on the “Y” chromosome. — False. The mutated genes are on the X chromosome, not the Y chromosome.
NCERT Extract:
Mendelian Disorders – “… Colour Blidness : 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.”