A couple both carries of sickle cell anaemia planning to get married, wants to know the chances of having anaemic progeny

Options

A. 1
B. 0.75
C. 0.5
D. 0.25

Answer

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anemia**:
- Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene. It is inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the mutated gene (one from each parent) to express the disease.

2. **Genotype of the Parents**:
- In this scenario, both parents are carriers of the sickle cell trait. This means their genotypes are:
- Parent 1: HbA HbS (carrier)
- Parent 2: HbA HbS (carrier)

3. **Setting Up a Punnett Square**:
- To determine the possible genotypes of their progeny, we can set up a Punnett square. The alleles from each parent will be placed along the top and side of the square.
- The alleles are:
- Parent 1: HbA (normal) and HbS (sickle)
- Parent 2: HbA (normal) and HbS (sickle)

4. **Filling in the Punnett Square**:
- The Punnett square will look like this:

| | HbA | HbS |
|-------|-------|-------|
| **HbA** | HbA HbA | HbA HbS |
| **HbS** | HbA HbS | HbS HbS |

5. **Analyzing the Results**:
- From the Punnett square, we can see the possible genotypes of the progeny:
- 1 HbA HbA (normal, not a carrier)
- 2 HbA HbS (carriers, but do not have the disease)
- 1 HbS HbS (sickle cell anemia)
- Therefore, the ratios are:
- 1 normal (HbA HbA)
- 2 carriers (HbA HbS)
- 1 affected (HbS HbS)

6. **Calculating the Probability of Affected Progeny**:
- The probability of having a child with sickle cell anemia (HbS HbS) is 1 out of 4, or 25%.

### Final Answer:
The chances of having an anemic progeny (sickle cell anemia) for the couple are **25%**.

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