Question

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:

a) Thalassemia major is dominant
b) The twins share identical genes
c) Thalassemia major is a spontaneous mutation
d) The twins have different genetic predispositions

Answer 1

The occurrence of thalassemia major in one of the dizygotic twins is likely because of different genetic predispositions, as both parents carry the gene for thalassemia minor. Each twin inherited a different combination of genes, which led to different expressions of the disease.

Step-by-step explanation:

The more serious case of thalassemia major most likely arose because (d) twins have different genetic predispositions. Thalassemia is a type of inherited anemia characterized by abnormal hemoglobin. Since Sanjay and Indira both have thalassemia minor, they carry the disease-causing gene. When they had their dizygotic (fraternal) twins, each child inherited a different combination of genes from their parents, resulting in one twin with thalassemia minor and one with thalassemia major. Unlike sickle-cell anemia, which provides some immunity to malaria due to a mutation in sickle-cell carriers, thalassemia does not confer any such immunity. Thalassemia major is typically the result of inheriting two mutated genes, one from each parent.