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JAMB Biology 2002 Question 47

Question 47

Chromosomes, DNA and Sex Linkage

If XN is the dominant allele for normal vision and Xn the recessive allele for colour-blindness, a boy with the genotype YXn will

  1. A.have normal vision
  2. B.be colour-blind
  3. C.be totally blind
  4. D.be a carrier of colour-blindness.
Show the answer and explanation

Answer: B (be colour-blind)

Explanation

A boy has only one X chromosome, so there is no second allele to mask the recessive one. With Xn he is colour-blind.