If both the parents are carriers for thalassemia which is an autosomal recessive disorder what are the chances of pregnancy resulting in an affected child

Options

A. `50%`
B. `25%`
C. `100%`
D. No chance

Answer

To determine the chances of a pregnancy resulting in an affected child when both parents are carriers for thalassemia, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Genetic Background**:
- Thalassemia is an autosomal recessive disorder. This means that an individual must inherit two copies of the recessive allele (small t) to express the disorder. If they inherit one normal allele (capital T) and one recessive allele (small t), they will be carriers but not affected.

2. **Identify the Genotypes of the Parents**:
- Since both parents are carriers, their genotypes can be represented as:
- Parent 1: Tt (heterozygous)
- Parent 2: Tt (heterozygous)

3. **Determine Possible Gametes**:
- Each parent can produce two types of gametes:
- Parent 1 can produce gametes: T (normal) and t (thalassemia)
- Parent 2 can produce gametes: T (normal) and t (thalassemia)

4. **Create a Punnett Square**:
- We can use a Punnett square to visualize the possible combinations of alleles from the parents:

| | T (from Parent 2) | t (from Parent 2) |
|-------|--------------------|--------------------|
| T (from Parent 1) | TT (normal) | Tt (carrier) |
| t (from Parent 1) | Tt (carrier) | tt (affected) |

5. **Analyze the Offspring Genotypes**:
- The possible genotypes of the offspring from the Punnett square are:
- TT: Normal (1 out of 4)
- Tt: Carrier (2 out of 4)
- tt: Affected (1 out of 4)

6. **Calculate the Probability of an Affected Child**:
- Out of the four possible combinations, only one combination results in an affected child (tt).
- Therefore, the probability of having an affected child is 1 out of 4, or 25%.

### Final Answer:
The chances of a pregnancy resulting in an affected child (thalassemia) when both parents are carriers is **25%**.

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