Q158 / 180 · AIIMS 2015 · Zoology

Which is genetically not possible?

  • Correct answer
    A
    Haemophilic father transfers the haemophilic gene to his son.
  • B
    Haemophilic father transfers the haemophilic gene to his daughter.
  • C
    Carrier mother transfers the haemophilic gene to her son.
  • D
    Carrier mother transfers the haemophilic gene to her daughter.

Solution

Haemophilia is a sex linked disease. It follows criss-cross inheritance in which father does not pass the sex-linked allele of a trait to his son. The same is passed to the daughter, from where it reaches the grandson, i.e., diagynic. It is because the males have only one $\mathrm{X}$-chromosome which is transferred to the female offspring. Only Y-chromosome of the father is transferred to the male offspring but this sex chromosome does not carry the allele for haemophilia. Mother passes the alleles of a sex-linked trait to both sons and daughters.

Hence, the correct answer is option: 'A'.

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