Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their twenties. How likely is it for a woman to have this condition?

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Women have two X chromosomes, so they can be either carriers or affected with Duchenne muscular dystrophy. However, since it is a recessive X-linked condition, a woman would need to have two copies of the recessive allele (one from each carrier parent) to have the condition. A carrier mother has a 50% chance of passing on the recessive allele to each of her offspring, regardless of their sex. An affected father would pass on his X chromosome with the recessive allele to all of his daughters, but none of his sons. Therefore, the daughters of an affected father and a carrier mother would have a 50% chance of inheriting the recessive allele from their mother and a 100% chance of inheriting it from their father. The combination of these two probabilities would result in a 50% chance of having the condition.

Duchenne Muscular Dystrophy Is a Serious Condition Caused by a Recessive