Question

question 6
the mother and father of a male hemophiliac (a recessive x - linked disorder ( = x^{h} )) have normal health. what is the mothers genotype?
( \bigcirc x^{h}y )
( \bigcirc x^{h}x^{h} )
( \bigcirc x^{h}x^{h} )
( \bigcirc x^{h}y )
( \bigcirc x^{h}x^{h} )

Explanation:

• Hemophilia is a recessive X - linked disorder. Males have the sex chromosomes \(XY\). A male hemophiliac has the genotype \(X^{h}Y\).
• The father of the hemophiliac male has normal health. Since males pass on their \(Y\) chromosome to their sons (and an \(X\) chromosome to their daughters), the father's genotype is \(X^{H}Y\) (because he is healthy and has only one \(X\) chromosome).
• The mother of the hemophiliac male has normal health. Females have the sex chromosomes \(XX\). The son gets his \(X\) chromosome from his mother. Since the son has the \(X^{h}\) (hemophilia - causing) allele, and the mother is healthy (so she must have at least one normal \(X^{H}\) allele), the mother must be a carrier. A carrier female has one normal allele (\(X^{H}\)) and one recessive (hemophilia - causing) allele (\(X^{h}\)), so her genotype is \(X^{H}X^{h}\).

Answer:

\(X^{H}X^{h}\) (the fifth option in the given list)