Alpha-thalassemia is most commonly found in which geographic regions?

• A. Southeast Asia and Africa
• B. Northern Europe
• C. Scandinavia
• D. North America

Answer: (A)

Alpha-thalassemia arises from deletions of alpha-globin genes on chromosome 16, and its frequency varies by historical malaria exposure. In populations where malaria was common, carriers gained some protection against severe malaria, so the allele persisted and became relatively common. This makes Southeast Asia and many parts of Africa regions with the highest prevalence. Regions with little historical malaria, like Northern Europe and Scandinavia, show much lower frequencies, and North America has variable frequencies due to diverse ancestry but generally not as high as malaria-endemic areas.