Question

Over 10 million Americans are heterozygous for the allele for cystic fibrosis, while about 30,000 people with homozygous recessive genotype have the disease. Cystic fibrosis results from a deficiency of a chloride-ion channel protein usually found in the membranes of cells lining the airway passages. Carriers produce a sufficient amount of the channel protein to avoid disease symptoms. The allele that prevents the disease in carriers is a ______ allele, and the one that causes the disease is a ______ allele?

1) dominant, recessive
2) recessive, dominant
3) homozygous, heterozygous
4) heterozygous, homozygous

Answer 1

The allele preventing cystic fibrosis in carriers is a dominant allele, while the allele causing the disease is a recessive allele. Thus, the answer is 1) dominant, recessive.

Step-by-step explanation:

Over 10 million Americans are heterozygous for the allele for cystic fibrosis, while about 30,000 people with the homozygous recessive genotype have the disease. In the context of cystic fibrosis, the allele that prevents the disease in carriers is a dominant allele, and the one that causes the disease when present in a homozygous recessive state is a recessive allele. Therefore, the answer to the student's question is 1) dominant, recessive.

Cystic fibrosis is an example of an autosomal recessive disorder, meaning that the disease manifests when an individual has two copies of the defective allele. A heterozygous individual, or carrier, possesses one copy of the normal allele and one copy of the recessive allele but does not exhibit symptoms of the disease. Individuals with cystic fibrosis have two recessive alleles (homozygous recessive), which lead to a deficiency in the proper functioning of the chloride-ion channel protein.