As a genetic counselor, you routinely advise couples about the possibility of genetic disease in their offspring based on their family histories. This morning you met with an engaged couple, both of whom are phenotypically normal. The man, however, has a brother who died of Duchenne-type muscular dystrophy, an X-linked condition that results in death before the age of 20. The allele responsible for this disease is recessive. His prospective bride, whose family has no history of the disease, is worried that the couple’s sons or daughters might be afflicted.
How would you advise this couple?
The sister of the man is also planning to marry. How would you advise her?

They should marry without any fear

Explanation:

It is given that the allele for Duchenne-type muscular dystrophy is X-linked recessive disease which means it can occurs in male only  if its X chromosome carries the recessive trait.

While in female, this disease can occur only when both the X chromosomes carry the recessive trait. If there is only one X chromosomes that carry the recessive trait, the mother will act as a carrier.

Now, the man is phenotypically normal thus his X chromosome do not carry recessive trait for Duchenne-type muscular dystrophy

And the woman he is planning to marry has no such family history.  This means she also has normal genotype.

Hence, the couple should not be worried  

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