Duchenne Muscular Dystrophy (DMD) is an X-linked recessive trait that causes muscular weakness, deterioration of muscle tissue, and loss of coordination. The allele for DMD is represented by Xd and the normal allele is represented by XD . Neither parent has DMD, but both of their sons express the trait. What are the genotypes of the parents?

The correct answer is - XDXd and XD Y

Explanation:

Sex-linked disorders are the disorders that are expressed only when there is two copy of the mutated allele or have not masked by the dominant allele of the gene. In DMD, the dominant allele is XD and the mutated allele is Xd. To express it there are the following genotype possible-

in women XdXd, and in men XdY, so these two genotypes are not possible for the parents in this case. If a mutated allele is present with the dominant allele it will be considered as carrier women but diseased will not be found in them.

So the correct genotype would be

mother: XDXd ( a carrier woman)

father : XDY (normal man)

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