KCET · BIOLOGY · STD 12 - 4. Principles of Inheritance and Variation

Sickle cell anaemia is caused due to the substitution of

A valine at the \(6^{\text {th }}\) position of beta globin chain by glutamine
B valine at the \(6^{\text {th }}\) position of alpha globin chain by glutamic acid
C glycine at the \(6^{\text {th }}\) position of alpha globin chain by glutamic acid
D glutamic acid at the \(6^{\text {th }}\) position of beta globin chain by valine

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Answer & Solution

Correct Answer

(D) glutamic acid at the \(6^{\text {th }}\) position of beta globin chain by valine

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Detailed explanation

(D) glutamic acid at the \(6^{\text {th }}\) position of beta globin chain by valine,
Sickle-cell anemia is an autosomal hereditary disorder in which the erythrocytes become sickle shaped under oxygen deficiency as during strenuous exercise and at high altitudes. S differs from normal haemoglobin- A in only one amino acid - \(6^{\text {th }}\) amino acid of \(\beta\)-chain, glutamic acid, is replaced by valine.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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