Final answer:
Autosomal recessive inheritance is a genetic pattern where disorders are expressed only when two copies of a recessive allele are inherited. An example is cystic fibrosis, where carriers have a 25 percent chance of passing the disease to their child if both parents are carriers. Carriers do not show symptoms but can pass the disorder to their offspring.
Step-by-step explanation:
Understanding Autosomal Recessive Inheritance
Autosomal recessive (AR) inheritance is the most common form of genetic inheritance for disorders that are located on the autosomes, which consist of the 22 non-sex determining chromosome pairs in humans. In this pattern, both parents must carry one copy of the mutated gene in order for a child to present with the disorder. As the name suggests, it follows a recessive pattern, meaning that the disease traits are only expressed when an individual has two copies of the recessive allele.
An example of autosomal recessive disorder is cystic fibrosis (CF), a condition characterized by the buildup of thick mucus in the lungs and digestive tract. With parents who are carriers (heterozygous for the trait), there is a 25 percent chance that a child will inherit CF. This reflects the classic 3:1 Mendelian ratio of dominant to recessive inheritance, suggesting a child has a 25 percent chance of having the disease, a 50 percent chance of being a carrier like their parents, and a 25 percent chance of neither carrying nor expressing the disease.
Carriers of an autosomal recessive disorder typically do not show symptoms because their second allele is normal and compensates for the recessive mutated allele. However, they can pass the mutated gene to their offspring, who might inherit the disorder if the other parent is also a carrier.