Mr. and Mrs. R have two other children, a son with beta-thalassemia minor and a

Question

Mr. and Mrs. R have two other children, a son with beta-thalassemia minor and a daughter with beta-thalassemia major.
Their son has married a healthy woman. They have three children: a boy with beta-thalassemia minor, a healthy girl, and a healthy boy.

Family trees like this are often represented graphically. Using this chart for reference, identify which figure most accurately represents Mr. R's family.

Choose the best answer.

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Genetic notation relevant to this problem beta-thalassemia allele normal allele Heterozygous male (beta-thalassemia minor: BN) Homozygous male (beta-thalassemia major BB) OHeterozygous female (beta-thalassemia minor: BN) Homozygous female (beta-thalassemia major: BB) HTOAman and a woman marry and have a son 0 |an

Explanation / Answer

Beta thalassemia follows autosomal Recessive pattern of inheritance.

To work this out, first we need to know that beta thalassemia minor is a Heterozygous condition and beta thalassemia major is a homozygous condition.

Thus, Mr R's son (thalassemia minor) is BN

Mr R's daughter (thalassemia major) is BB

Thus, two situations can be possible here

Furthermore, if their beta thalassemia minor son marries a healthy woman and they have 4 children, there's a chance that 1/4 of those children will have beta thalassemia minor.

Thus the diagram which most accurately represents this situation is the first one. ( The last one is also possible but the first one is more likely)

Mother/Father B N B BB BN N BN NN

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