Sanjay and Indira have thalassemia minor.Their young daughters are dizygotic (fraternal)twins.Malonie has thalassemia minor like her parents,but Jewel has the more severe thalassemia major.The more serious case most likely arose because

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Thalassemia major is inherited recessively, meaning that an individual must inherit two copies of the mutated beta globin gene from both parents to develop the more severe form of the disease. Sanjay and Indira both have thalassemia minor, which means they each carry one copy of the mutated gene and one wild-type gene. The chance of their dizygotic twins inheriting two copies of the mutated gene is 25%. Malonie inherited one mutated gene from each parent, resulting in her having thalassemia minor like her parents. However, Jewel inherited two copies of the mutated gene, resulting in her having thalassemia major. Therefore, the most likely explanation for the more severe form of the disease in Jewel is that she inherited two recessive mutant alleles in the beta globin gene that cause thalassemia.

Sanjay and Indira Have Thalassemia Minor