Colour blindness is found more in males than in females because:
- AMales with a single affected X chromosome are colour blind
- BHeterozygous females are colour blind
- CMales with an affected Y chromosome are colour blind
- DThe affected X chromosome has a much higher affinity for the Y chromosome than the unaffected X chromosome
Show answer and explanation
Correct answer: (a) Males with a single affected X chromosome are colour blind
Explanation
Colour blindness is caused by a recessive gene on the X chromosome (sex-linked inheritance).
- A male (XY) has only one X chromosome. If it carries the faulty gene, there is no normal copy to mask it, so he is colour blind.
- A female (XX) is colour blind only if both her X chromosomes carry the gene. With one affected X, she is a carrier with normal vision.
The Y chromosome does not carry this gene, and an affected X chromosome has no special attraction to the Y.