If both parents are carriers for thalessemia, which is ai:, autosomal recessive disorder, what are the chan~e~ pregnancy resulting in an affected child?

Options

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

Answer

To solve the problem regarding the chances of having a child affected by thalassemia when both parents are carriers, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Genetic Condition**:
- Thalassemia is an autosomal recessive disorder. This means that a child must inherit two copies of the thalassemia gene (one from each parent) to express the disease.

2. **Identify the Genotypes 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 thalassemia allele.

3. **Set Up a Punnett Square**:
- Create a Punnett square to visualize the genetic combinations that can arise from the cross between the two parents (Tt x Tt).

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

4. **Analyze 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 by thalassemia) - 1 out of 4

5. **Calculate the Probability of an Affected Child**:
- The probability of having a child affected by thalassemia (tt) is 1 out of 4, or 25%.

6. **Conclusion**:
- Therefore, the chances of a pregnancy resulting in an affected child (with thalassemia) when both parents are carriers is **25%**.