What is a key characteristic of autosomal recessive disorders like cystic fibrosis?

In autosomal recessive disorders, such as cystic fibrosis, the key characteristic is that the phenotype is fully expressed only when both copies of the gene are mutated. This means that an individual must inherit two copies of the mutated gene—one from each parent—for the condition to manifest. If only one copy is mutated, the individual is typically considered a carrier and does not exhibit symptoms of the disorder.

The reason this characteristic is significant is that it informs both the genetics of the disease and the implications for family planning and genetic counseling. When both parents are carriers, there is a 25% chance with each pregnancy that their child will inherit both mutated alleles and express the disorder. This understanding is essential in managing and providing care for patients diagnosed with cystic fibrosis.

In contrast, carriers with only one mutated copy generally remain asymptomatic, which is a hallmark of autosomal recessive inheritance patterns.