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 or have the disorder. How can this be explained?
The child contracted the illness from another child when he was born.
The child developed the disorder when he was born; it is a result of a birth defect.
The genetic disorder formed from the mother's poor nutrition and prenatal care.
The genetic disorder is recessive, and can be carried by heterozygous individuals without ever being realized or identified.
The correct explanation is: The genetic disorder is recessive, and can be carried by heterozygous individuals without ever being realized or identified.
Cystic fibrosis is caused by a mutation in a gene called CFTR. It is an autosomal recessive disorder, which means that both copies of the gene must be mutated in order for the disorder to manifest. If both parents are carriers of the mutated gene (heterozygous), each has a 25% chance of passing on both mutated copies to their child, resulting in the child being affected by cystic fibrosis.
Even if no one in the family is known to be affected by or carry the disorder, it is still possible for both parents to be carriers without realizing it. This is because carriers of cystic fibrosis typically do not show any symptoms of the disorder and can lead normal lives. It is only when two carriers have a child together that there is a chance of the disorder being passed on.
Therefore, in the given scenario, it is likely that both parents are carriers of the cystic fibrosis gene and passed on the mutated gene to their child without realizing it.