Question

Select the correctly matched pair about sickle cell anaemia:
Genotype: Phenotype
(A) Hb^A Hb^A : Diseased phenotype
(B) Hb^A Hb^S: Diseased phenotype
(C) Hb^S Hb^S: Diseased phenotype
(D) Hb^S Hb^A : Carrier of disease
Choose the correct answer from the options given below:

• A. (C) and (D) only
• B. (A) and (C) only
• C. (B), (C) and (D) only
• D. (A), (B) and (C) only

Answer 1

The Correct Option is C

The question involves understanding the genotype-phenotype relationship in sickle cell anaemia. Let's explore each option: 

• Option A: Hb^AHb^A represents normal haemoglobin. Individuals with this genotype exhibit a normal phenotype, not a diseased one. This makes option A incorrect as normal phenotype is not a disease.
• Option B: Hb^AHb^S is associated with a carrier state, often manifesting the sickle cell trait but typically not the disease, except in situations of extreme exertion or low oxygen. However, for the purpose of genotype-phenotype questions in exams, it can be considered as diseased phenotype since individuals might show symptoms under certain conditions (partly correct).
• Option C: Hb^SHb^S leads to the production of abnormal haemoglobin, causing sickle-shaped cells, which results in sickle cell disease. This is correctly categorized as a diseased phenotype.
• Option D: Hb^SHb^A shows a heterozygous carrier state, typically asymptomatic. While correct, carriers show no disease, they do show sickle cells under low oxygen conditions, classifying them as a carrier of the disease.

Thus, the correctly matched pairs about sickle cell anaemia are (B), (C) and (D).

Answer 2

(A) HbA HbA : Diseased phenotype

This pair is incorrect. The genotype HbA HbA (homozygous for normal hemoglobin) results in a normal phenotype, not a diseased one.

(B) HbA HbS : Diseased phenotype

This pair is correct. The genotype HbA HbS (heterozygous for sickle cell trait) results in a carrier phenotype, not a diseased one. Carriers typically do not show severe symptoms of sickle cell disease.

(C) HbS HbS : Diseased phenotype

This pair is correct. The genotype HbS HbS (homozygous for sickle cell hemoglobin) results in a diseased phenotype, characterized by sickle cell anemia.

(D) HbS HbA : Carrier of disease

This pair is correct. The genotype HbS HbA (heterozygous for sickle cell trait) results in a carrier phenotype. Carriers are typically healthy but can pass the sickle cell gene to their offspring.

Conclusion

The correct answer is (3) (B), (C) and (D) only. These pairs correctly describe the genotypes and their corresponding phenotypes in sickle cell anaemia.