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?
a
The genetic disorder is recessive, and can be carried by heterozygous individuals without ever being realized or identified.
b
The child contracted the illness from another child when he was born.
c
The genetic disorder formed from the mother's poor nutrition and prenatal care.
d
The child developed the disorder when he was born; it is a result of a birth defect.
a
The genetic disorder is recessive, and can be carried by heterozygous individuals without ever being realized or identified.
Cystic fibrosis is an autosomal recessive genetic disorder, which means that an individual must inherit two copies of the defective gene (one from each parent) to exhibit the symptoms of the disease. Carriers of the disease, who have one normal allele and one defective allele (heterozygous), typically do not show any symptoms. It is possible for a child to be born with cystic fibrosis even if there are no known cases in the family for several generations because the faulty gene can be passed down silently through carriers until two carriers have a child together, with a 25% chance that their offspring will inherit the defective gene from both parents.