Unaffected male Affected male
Unaffected female
Affected female
oo
Figure 1. Incidence of protoporphyria in a particular family
Protoporphyria is a genetic disorder characterized by an extreme sensitivity to sunlight. One form of protoporphyria is caused by a mutation in
the ALAS2 gene that results in the accumulation of protoporphyrin, an organic compound, in the blood, liver, and skin. The pedigree in Figure 1 shows
the incidence of protoporphyria in a particular family.
Which of the following best describes the inheritance pattern illustrated in Figure 1 ?
Protoporphyria has an autosomal recessive inheritance pattern
O Protoporphyria has an X-linked dominant inheritance pattern
O Protoporphyria has an X-linked recessive inheritance pattern
O Protoporphyria has a mitochondrial inheritance pattern