Final answer:
When two heterozygous carriers for a recessive disease have children, each child has a 25% chance of inheriting two recessive alleles and therefore being affected by the disease, as shown by a Punnett square.
Step-by-step explanation:
Parents who are carriers for a recessive disease each have one copy of the recessive allele and one copy of the dominant allele, which means they are heterozygous for the trait. When two such carrier parents conceive a child, there is a 25% chance that the child will inherit two recessive alleles, resulting in the expression of the disease. A simple way to visualize this inheritance pattern is by creating a Punnett square.
In the Punnett square, the alleles from each parent are combined to show the potential genotypes of their offspring. Since each parent has one dominant (F) and one recessive (f) allele for the trait, their genotypes are represented as Ff.
This pattern of inheritance is typical for autosomal recessive disorders, such as cystic fibrosis, Tay-Sachs disease, and sickle-cell anemia. If the disease in question follows this inheritance pattern, the correct answer to the student's question is that each child has a 25% chance of inheriting two recessive alleles and the disease.