In an autosomal recessive disease, how many copies of the mutated gene are typically required for disease manifestation?

• A. Two copies
• B. One copy
• C. Three copies
• D. No copies

Answer: (A)

In autosomal recessive diseases, you need two mutated copies of the gene to show the disease. Each person has two copies of each autosomal gene, one from each parent. If you inherit a mutated copy from both parents, you have two defective copies and typically develop the condition. If you only inherit one mutated copy, you usually don’t show symptoms; you’re a carrier who can pass the mutation to offspring. The idea of three mutated copies isn’t how this inheritance pattern works, and having no mutated copies wouldn’t cause the disease. So, two copies are required for disease manifestation.