Problem
Glucose-6-phosphate dehydrogenase (G6PD) is encoded by an X-linked gene. G6PD loss-of-function mutations can lead to hemolysis on exposure to some drugs, fava beans, and other compounds. Electrophoresis of red blood cell hemolysates shows that some females have two G6PD bands, but males have a single band. Explain this observation and the possible pathological and genetic significance of the finding of two bands in an African American female.