How many copies of a mutated gene are required for an autosomal recessive disorder to manifest?

How many copies of a mutated gene are required for an autosomal recessive disorder to manifest?

• A. One copy
• B. Two copies
• C. Three copies
• D. Four copies

Answer: (B)

An autosomal recessive disorder manifests when an individual has two copies of a mutated gene, one inherited from each parent. This means that both alleles at a specific locus on the autosome must exhibit the mutation for the phenotype to be expressed. Individuals with one mutated gene and one normal gene are considered carriers and typically do not show symptoms of the disorder, as the normal allele can compensate for the mutated allele.

In summary, the presence of two copies of the mutated gene is necessary for the autosomal recessive condition to present clinically, which is foundational in understanding inheritance patterns and genetic counseling for families affected by such disorders.