Question

Muscular Dystrophy is a recessive disorder that is carried on the X chromosome. A woman who
is a carrier for this disorder marries a man who does not have this trait.
A) allele key: ____ = normal ____ = muscular dystrophy
B) parent genotypes: mom = ____ dad = ____
C) punnet square:

Answer 1

A)
Allele key: X^N = normal (dominant) , X^d = muscular dystrophy (recessive)

B)
Parent genotypes: mom = X^N X^d (carrier) , dad = X^N Y (unaffected)

C)
Punnett square (mother gametes on left, father on top):

X^N | Y
--------------------------
X^N | X^N X^N | X^N Y
| (female, | (male,
| normal) | normal)
--------------------------
X^d | X^d X^N | X^d Y
| (female, | (male,
| carrier) | affected)

Genotype probabilities: 25% X^N X^N, 25% X^N X^d, 25% X^N Y, 25% X^d Y.
Phenotype: 25% unaffected non-carrier daughter, 25% carrier daughter, 25% unaffected son, 25% affected son.