It is said, that the harmful alleles get eliminated from population over a period of time, yet sickle-cell anaemia is persisting in human population. Why?

Explanation

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anemia**:
- Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene. This mutation leads to the production of abnormal hemoglobin, known as hemoglobin S (HbS), which can cause red blood cells to become misshapen (sickle-shaped).

2. **Harmful Alleles and Their Elimination**:
- Typically, harmful alleles (like those causing sickle cell anemia) would be expected to decrease in frequency within a population over time due to natural selection, as individuals with severe forms of the disease (homozygous HbS/HbS) often face higher mortality rates.

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