Question

which couple could have a boy with duchenne muscular dystrophy (dmd)?
○ a male with dmd and a homozygous dominant female
○ a male without dmd and a carrier female
○ none of these
○ all of these
○ a male without dmd and a homozygous dominant female

Explanation:

Duchenne muscular dystrophy (DMD) is an X - linked recessive disorder. Let's analyze each option:

• Option A: A male with DMD has the genotype \(X^{d}Y\) (where \(d\) represents the mutant allele for DMD). A homozygous dominant female has the genotype \(X^{D}X^{D}\). Their children: All daughters will be \(X^{D}X^{d}\) (carriers) and all sons will be \(X^{D}Y\) (normal).
• Option B: A male without DMD has the genotype \(X^{D}Y\). A carrier female has the genotype \(X^{D}X^{d}\). Using a Punnett square (\(X^{D}\times X^{D}X^{d}\)):
• For sons: There is a \(50\%\) chance of getting \(X^{D}Y\) (normal) and a \(50\%\) chance of getting \(X^{d}Y\) (with DMD).
• Option E: A male without DMD (\(X^{D}Y\)) and a homozygous dominant female (\(X^{D}X^{D}\)): All children (both sons and daughters) will be normal. Sons will be \(X^{D}Y\) and daughters will be \(X^{D}X^{D}\).

So, only the couple in option B (a male without DMD and a carrier female) has a chance of having a boy with DMD.

Answer:

B. a male without DMD and a carrier female