A child is born with cystic fibrosis, an inherited recessive disorder. No one in the family (on either side) for several generations is known to carry the gene or have the disorder. How can this be explained? a The genetic disorder formed from the mother's poor nutrition and prenatal care. b There was a mutation in the DNA, either in one of the gametes or the fertilized egg. c The child contracted the illness from another child when he was born. d The child developed the disorder when he was born; it is a result of a birth defect.

Answer 1

The most accurate explanation for a child being born with cystic fibrosis when no one in the family has a known history of the disorder is:

b. There was a mutation in the DNA, either in one of the gametes or the fertilized egg.

Cystic fibrosis is caused by a mutation in the CFTR gene, which is inherited in an autosomal recessive manner. This means that both parents must carry at least one copy of the mutated gene for a child to inherit the disorder. However, it is possible for a mutation to occur spontaneously in the DNA of a gamete (sperm or egg) or during the early cell divisions after fertilization. This could lead to the child being the first in the family to have the disorder, even if there are no known carriers in the family history.

The other options do not accurately reflect how genetic disorders like cystic fibrosis arise:

• a. Poor nutrition and prenatal care do not cause genetic disorders; they can affect overall health but not the inherited genetic conditions.
• c. Cystic fibrosis is not contagious and cannot be contracted from another child.
• d. Cystic fibrosis is a genetic disorder present at birth and not something that develops due to a birth defect.