Question

Sickle-cell anemia is a genetic disorder of the blood in which the shape of red blood cells is distorted, resulting in a variety of health problems. The allele for normal blood cell production (H) is dominant to the allele for sickle cell production (h).

If one parent has sickle-cell anemia and the other parent is a carrier, what is the probability that their child will have sickle-cell anemia?

Hint: Use the Punnett square below to help you.
H h
h ? ?
h ? ?
A.
50%
B.
100%
C.
25%
D.
75%

Answer 1

To determine the probability that the child will have sickle-cell anemia, we can set up a Punnett square using the genotypes of the parents.

1. **Identifying the genotypes:**
- The parent with sickle-cell anemia has the genotype **hh** (since they express the sickle-cell trait).
- The carrier parent has the genotype **Hh** (since they carry one normal allele and one sickle-cell allele).

2. **Setting up the Punnett square:**

```
H h
______________
h | Hh | hh |
|___________|
h | Hh | hh |
|___________|
```

3. **Filling in the Punnett square:**
- The combinations from the cross are:
- Hh (normal, carrier)
- Hh (normal, carrier)
- hh (sickle-cell anemia)
- hh (sickle-cell anemia)

4. **Counting the outcomes:**
- Hh (normal, carrier): 2 outcomes
- hh (sickle-cell anemia): 2 outcomes

5. **Probability of having sickle-cell anemia:**
- There are a total of 4 outcomes.
- Out of these, 2 outcomes (hh) result in sickle-cell anemia.
- Therefore, the probability is \( \frac{2}{4} = \frac{1}{2} \) or 50%.

So, the answer is **A. 50%**.