Let's break down the steps to solve the question:
1. Identify the Genetic Condition: Tay-Sachs Disease (TSD) is an autosomal recessive disorder. This means that for a child to have TSD, they must inherit two copies of the recessive allele (one from each parent).
2. Determine the Genotype of the Parents: Since both parents are unaffected carriers, their genotype must be heterozygous for the TSD allele. We'll use "A" to represent the normal allele and "a" to represent the TSD allele. Hence, the genotype of both parents is Aa.
3. Construct a Punnett Square: The Punnett square is a tool used to predict the probability of offspring inheriting particular genotypes from their parents.
- The possible alleles from one parent (Aa) are A and a.
- The possible alleles from the other parent (Aa) are also A and a.
- The Punnett square is constructed as follows:
```
A a
_________
A | AA Aa |
_________
a | Aa aa |
_________
```
4. Analyze the Punnett Square: From the Punnett square, we can see the possible genotypes of their offspring.
- There is one AA (normal) combination.
- There are two Aa (carrier) combinations.
- There is one aa (affected by TSD) combination.
5. Calculate the Probabilities:
- AA (Normal): 1 out of 4 squares = 25%
- Aa (Carrier): 2 out of 4 squares = 50%
- aa (Affected by TSD): 1 out of 4 squares = 25%
6. Conclude the Answer: Since the probability that each child would inherit the genotype aa, which results in TSD, is 25%, the correct statement is:
D There is a 25% chance that each child would have the disease.
By following these steps, we determine that the likelihood of a child inheriting Tay-Sachs Disease given both parents are unaffected carriers is indeed 25%.
