If mother and father are both sickle cell carriers, what are the chances that the child will not have the trait?

Answer

To determine the chances that a child will not have the sickle cell trait when both parents are carriers, we can follow these steps:

### Step 1: Understand the Genetics of Sickle Cell Anemia
Sickle cell anemia is caused by a mutation in the hemoglobin gene and is inherited in an autosomal recessive manner. This means that a child must inherit two copies of the mutated gene (one from each parent) to express the disease.

### Step 2: Identify the Genotypes of the Parents
Both parents are carriers of the sickle cell trait. Their genotypes can be represented as:
- Mother: HBA HBS (carrier)
- Father: HBA HBS (carrier)

### Step 3: Set Up a Punnett Square
To find the possible genotypes of the offspring, we can use a Punnett square. The alleles from each parent are placed on the top and side of the square:

| | HBA | HBS |
|-------|------|------|
| **HBA** | HBA HBA | HBA HBS |
| **HBS** | HBA HBS | HBS HBS |

### Step 4: Determine the Possible Offspring Genotypes
From the Punnett square, we can see the possible genotypes for the children:
1. HBA HBA (normal, not a carrier)
2. HBA HBS (carrier)
3. HBA HBS (carrier)
4. HBS HBS (affected by sickle cell anemia)

### Step 5: Count the Outcomes
Now, let's count the outcomes:
- 1 child with genotype HBA HBA (normal)
- 2 children with genotype HBA HBS (carriers)
- 1 child with genotype HBS HBS (affected)

### Step 6: Calculate the Probability
To find the probability that a child will not have the sickle cell trait, we consider the outcomes that do not express the trait:
- HBA HBA (normal): 1 outcome
- HBA HBS (carrier): 2 outcomes

Total outcomes = 4 (1 normal + 2 carriers + 1 affected)

The probability that a child will not have the sickle cell trait is:
\[ \text{Probability} = \frac{\text{Number of non-affected outcomes}}{\text{Total outcomes}} = \frac{3}{4} = 75\% \]

### Conclusion
The chances that the child will not have the sickle cell trait are 75%.

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