Which statement best describes autosomal recessive inheritance?

• A. Affected person has a mutation in both copies of the gene in each cell.
• B. Affected person has a mutation in one copy of the gene.
• C. The trait is always transmitted from an affected parent to all children.
• D. The condition occurs only in males.

Answer: (A)

Autosomal recessive inheritance requires two mutated copies of the gene for the disease to be expressed. An affected person has mutations in both copies of the gene in each cell, becoming homozygous recessive. This happens when they inherit one mutated allele from each parent, and those parents are typically carriers who have one normal and one mutated copy but usually show no symptoms. Because the gene is on an autosome, males and females are affected with equal frequency, and the trait can appear in generations if two carriers have children. It’s not transmitted to all children from an affected parent; if two carriers mate, about a quarter of their children are affected, half are carriers, and a quarter are unaffected. The statement that the trait occurs only in males describes X-linked inheritance, not autosomal.