Question

Sol.(a) [Key Concept: DMD — X-linked Recessive in Females] DMD is almost never seen in girls because FEMALES NEED TWO COPIES of an X-linked recessive allele to express it. A girl would need both X chromosomes to carry the DMD mutation (X^d X^d) — an extremely rare event (she would need to have a carrier mother and an affected father). Most females with one copy are healthy carriers (X^D X^d). Males with only one X chromosome express the condition if they have even one copy (X^d Y).