Why are individuals who are heterozygous for the cystic fibrosis allele unaffected by the disease?

• A. Heterozygous individuals have a mutation that prevents the disease.
• B. They have one normal allele that produces enough functional protein.
• C. The cystic fibrosis allele is only expressed in homozygous individuals.
• D. The cystic fibrosis allele is dominant, so it does not express the disease.

Answer: (B)

Verified step by step guidance

1. Understand the concept of alleles: Alleles are different forms of a gene. In the case of cystic fibrosis, there are two alleles - one normal and one mutated.
2. Learn about heterozygosity: A heterozygous individual has two different alleles for a particular gene, one from each parent. For cystic fibrosis, this means having one normal allele and one mutated allele.
3. Explore protein production: The normal allele produces a functional protein that is necessary for normal cellular function. This protein is called CFTR (Cystic Fibrosis Transmembrane Conductance Regulator).
4. Consider the effect of the normal allele: In heterozygous individuals, the presence of one normal allele is sufficient to produce enough functional CFTR protein to prevent the symptoms of cystic fibrosis.
5. Understand expression in homozygous individuals: Cystic fibrosis manifests in individuals who are homozygous for the mutated allele, meaning they have two copies of the mutated allele and no normal allele to produce functional CFTR protein.