What type of disorder requires two copies of a mutated gene to be present for expression?

• A. X-linked disorders
• B. Autosomal dominant disorders
• C. Autosomal recessive disorders
• D. Chromosomal abnormalities

Answer: (C)

Autosomal recessive disorders are characterized by the requirement of two copies of a mutated gene for the disorder to manifest. In this type of genetic inheritance, an individual must inherit one mutated copy of the gene from each parent to express the condition. If a person has only one mutated gene and one normal gene, they are typically considered a carrier but do not show any symptoms of the disorder themselves.

In contrast, autosomal dominant disorders require only one copy of the mutated gene for the disorder to present, meaning that individuals who inherit just one altered gene will typically display the characteristics of the disorder, regardless of the second gene's status. X-linked disorders usually affect males more severely due to the presence of only one X chromosome, requiring a mutated gene on that X chromosome to exhibit the disorder, while females with one mutated gene are often carriers. Chromosomal abnormalities refer to alterations in the structure or number of chromosomes themselves and do not fit the description of requiring two mutated gene copies to express a trait.

Thus, the clarity of autosomal recessive inheritance, which mandates dual gene mutations, correctly identifies this type of genetic disorder as the focus of the question.