Muscular dystrophy is a sex-linked recessive disorder. A man with muscular dystrophy morries a woman who doesn't have this disease Half of their ddoghters and half of their sons develop this disease. What is the genotype of the mother? x^n x^Nx^n x^N

The correct answer is $x^{N}x^{n}$.<br /><br />Muscular dystrophy is a sex-linked recessive disorder, which means that the gene responsible for this disorder is located on the X chromosome. In this case, the man with muscular dystrophy has the genotype $x^{n}y$, where $x^{n}$ represents the X chromosome carrying the gene for muscular dystrophy and $y$ represents the Y chromosome.<br /><br />Since the mother does not have the disease, she must have at least one normal X chromosome. However, since half of their daughters and half of their sons develop the disease, the mother must be a carrier of the gene for muscular dystrophy. Therefore, her genotype is $x^{N}x^{n}$, where $x^{N}$ represents the normal X chromosome.