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.
100%
B.
75%
C.
25%
D.
50%
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Answer 1

To determine the probability that their child will have sickle-cell anemia, we need to set up a Punnett square using the alleles from the parents.

1. One parent has sickle-cell anemia, which means their genotype is **hh** (they have two recessive alleles).
2. The other parent is a carrier, which means their genotype is **Hh** (one dominant allele for normal cells and one recessive allele for sickle cells).

Now we can build the Punnett square:

```
H h
----------------
h | Hh hh
----------------
h | Hh hh
```

From the Punnett square:
- 50% of the offspring (Hh) will be carriers, but not have sickle-cell anemia.
- 50% of the offspring (hh) will have sickle-cell anemia.

Thus, the probability that their child will have sickle-cell anemia is **50%**.

The correct answer is **D. 50%**.