Which of the following traits requires two recessive alleles for expression?

Which of the following traits requires two recessive alleles for expression?

• A. Huntington's disease
• B. Height in pea plants
• C. Cystic fibrosis
• D. Brown eye color

Answer: (C)

Cystic fibrosis is a genetic disorder that indeed requires two recessive alleles for its expression. The condition is caused by mutations in the CFTR gene, which leads to the production of a faulty protein that is essential for regulating the movement of salt and water in and out of cells. For a person to exhibit the symptoms of cystic fibrosis, they must inherit one mutated CFTR allele from each parent, meaning they possess two copies of the recessive allele. This is characteristic of autosomal recessive inheritance, where the presence of two recessive alleles is necessary for the phenotype associated with the disorder to manifest. In contrast, Huntington's disease is caused by a dominant allele, meaning only one copy of the allele is required for the disease to be expressed. Height in pea plants is a trait that can be influenced by multiple genes and may not fit the simple recessive requirement stated in the question. Brown eye color is often influenced by multiple alleles and can involve both dominant and recessive interactions, but the trait itself does not require two recessive alleles to be expressed. Thus, cystic fibrosis distinctly qualifies as the trait that necessitates two recessive alleles for expression.

Cystic fibrosis is a genetic disorder that indeed requires two recessive alleles for its expression. The condition is caused by mutations in the CFTR gene, which leads to the production of a faulty protein that is essential for regulating the movement of salt and water in and out of cells.

For a person to exhibit the symptoms of cystic fibrosis, they must inherit one mutated CFTR allele from each parent, meaning they possess two copies of the recessive allele. This is characteristic of autosomal recessive inheritance, where the presence of two recessive alleles is necessary for the phenotype associated with the disorder to manifest.

In contrast, Huntington's disease is caused by a dominant allele, meaning only one copy of the allele is required for the disease to be expressed. Height in pea plants is a trait that can be influenced by multiple genes and may not fit the simple recessive requirement stated in the question. Brown eye color is often influenced by multiple alleles and can involve both dominant and recessive interactions, but the trait itself does not require two recessive alleles to be expressed. Thus, cystic fibrosis distinctly qualifies as the trait that necessitates two recessive alleles for expression.