If XN is the dominant allele for normal vision and Xn the recessive allele for colour blindness, a boy with the genotype YXn will be
The correct answer is B. Be colour blind.
Since the boy has the genotype YXn:
- The Y chromosome indicates that he is male.
- The Xn allele is the recessive allele for colour blindness.
As a male, he only has one X chromosome, and since it carries the Xn allele, he will express the trait of colour blindness. Males are more likely to express X-linked recessive traits, such as colour blindness, because they have only one X chromosome. Females, on the other hand, would need to inherit two copies of the Xn allele (one from each X chromosome) to express colour blindness.
The other options are not correct:
A. The boy will not have normal vision because he has the Xn allele.
C. The boy will not be totally blind; colour blindness is a specific visual impairment, not total blindness.
D. The boy cannot be a carrier of colour blindness because he is male and only has one X chromosome. Carriers are typically females who have one Xn allele and one normal allele (XN).
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