Question

Sometimes a gene which carries a major disadvantage in homozygous state confers an advantage in the heterozygous condition. Explain by giving a suitable example.

• A. Down's syndrome
• B. Sickle cell anemia
• C. Cystic fibrosis
• D. None of the above

Answer 1

Answer: (B)

Sickle cell anemia

Sometimes a gene which carries a major disadvantage in homozygous state confers an advantage in the heterozygous condition. An example for this is of sickle cell anemia. The average age of an individual with homozygous state for sickle-cell anemia is around 20 years. The individual without defective gene for sickle-cell anaemia are sensitive towards malaria. However, the individual having heterozygous condition for sickle-cell anemia are resistant to malaria. Due to abnormal haemoglobin, the malarial parasite will not harm the person. Hence, in this heterozygous condition, the person is neither suffering from sickle cell anemia nor is he affected by malaria.

Thus, the correct answer is 'Sickle cell anemia.'