Concept:Colour blindness is an
X-linked recessive trait, so the idea of a “carrier” depends on the sex chromosomes of the individual.
Explanation:The gene for colour blindness is recessive and located on the
X chromosome.
A male has only one
X chromosome.
If a male inherits the defective allele, he will express colour blindness.
Therefore, a male cannot be a carrier without being affected.
So option B, “Males are often carriers”, is not correct.
A female has two
X chromosomes.
If a female has the defective allele on one
X chromosome and a normal allele on the other
X chromosome, she becomes a carrier.
Such a female does not show colour blindness but can pass the allele to her children.
So option C, “females are not carriers”, is also not correct.
Answer:Options B and C are not correct.