Question

A woman has an X-linked condition on one o f her X-chromosomes. This chromosome can be inherited by

• A. Only grand children
• B. Only sons
• C. Only daughters
• D. Both (b) and (c)

Answer 1

Answer: (D)

In the given problem, the woman has an $X$-linked condition and she can transmit the carrier allele to both her son and daughter. The resulting son will affected because $X$-linked disorder always affect males as males contain a single $X$-chromosome. The daughter offspring will be a carrier, but not diseased because females are affected by $X$-linked disorder in homozygous recessive condition only, i.e. two recessive alleles are required.

Hence, out of the $4$ offspring possible $25\%$ of sons are diseased and $25\%$ are normal. Similarly, $50\%$ daughters normal out of which half are carriers.