Thalassemia is a hereditary disease of the blood of humans resulting in anemia. Severe anemia (Thalassemia major) is found in homozygous (TMTM) and a milder form (Thalassemia minor) is found in heterozygous (TMTN). Normal individuals are homozygous (TNTN). If all individuals of Thalassaemia major die before sexual maturity, what fraction of the adult F₁ from marriages of minors with minors would be expected to be anemic?
Thalassemia is a hereditary disease of the blood of humans resulting in anemia. Severe anemia (Thalassemia major) is found in homozygous (TMTM) and a milder form (Thalassemia minor) is found in heterozygous (TMTN). Normal individuals are homozygous (TNTN). If all individuals of Thalassaemia major die before sexual maturity, what fraction of the adult F₁ from marriages of minors with minors would be expected to be anemic?
Answer:
If all individuals with Thalassemia major die before sexual maturity, the fraction of the adult F1 from marriages of minors with minors that would be expected to be anemic would be 0.25. This is because, in such a marriage, each parent is a carrier of the trait (TMTN) and the offspring of such a marriage would thus be expected to be in a 1:2:1 ratio of normal individuals (TNTN): carriers (TMTN): individuals with Thalassemia major (TMTM). Since those individuals with Thalassemia major would not have survived to adulthood, the fraction of anemic individuals would be 0.25 (1/4).
Explanation:
If all individuals of Thalassemia major die before sexual maturity, the expected fraction of anemic individuals in the F1 generation of marriages between Thalassemia minors would be 0.25, or 25%. This is because, when two Thalassemia minors are married, the genotypes of their offspring will be 25% TT (Thalassemia major), 50% TN (Thalassemia minor), and 25% NN (normal individuals). Since only the TT individuals will be anemic, 25% of the offspring will be anemic.
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