If both the parents are carriers of autosomal r recessive disorder thalassemia , what are the chances of pregnancy resulting in an affected child

Options

A. 1
B. No chance
C. 0.5
D. 0.25

Answer

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

### Step-by-Step Solution:

1. **Understanding the Genetics of Thalassemia**:
- Thalassemia is an autosomal recessive disorder. This means that an individual must inherit two copies of the mutated gene (one from each parent) to express the disorder.

2. **Genotype of the Parents**:
- Since both parents are carriers, their genotypes can be represented as "Tt", where "T" is the normal allele and "t" is the allele for thalassemia.

3. **Setting Up a Punnett Square**:
- To find the probability of their children inheriting the disorder, we can set up a Punnett square. The possible gametes from each parent are "T" and "t".

```
T t
---------------
T | TT | Tt |
|-------|-------|
t | Tt | tt |
---------------
```

4. **Analyzing the Offspring Genotypes**:
- From the Punnett square, we can see the possible genotypes of the offspring:
- TT (normal) - 1 out of 4
- Tt (carrier) - 2 out of 4
- tt (affected) - 1 out of 4

5. **Calculating the Probability of an Affected Child**:
- The probability of having an affected child (tt) is 1 out of 4, or 0.25.

### Final Answer:
The chances of a pregnancy resulting in an affected child (thalassemia) when both parents are carriers is **0.25**.

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