Final answer:
Autosomal recessive disorders, such as cystic fibrosis, require individuals to inherit two copies of a recessive allele to express the condition. Carriers have one normal and one mutated allele but do not show symptoms. The chance of offspring inheriting such a disorder from two carrier parents follows a 3:1 dominant to recessive ratio.
Step-by-step explanation:
Autosomal recessive disorders occur when a person inherits two copies of a recessive allele for a specific trait. An example of such a disorder is cystic fibrosis (CF), characterized by the production of thick mucus in the lungs and digestive tract.
Carriers of an autosomal recessive disorder, such as the CFTR gene in CF, have one normal allele and one mutated allele, but they do not present symptoms; they may pass the recessive allele to their offspring. For a child to express the disorder, they must inherit the recessive allele from both parents. With two carrier parents, there is a 25 percent chance of the child inheriting the disorder, following a 3:1 ratio of dominant to recessive inheritance, as seen in Mendelian genetics.
The inheritance pattern can be analyzed using a Punnett square, which helps to predict the probability of genotypic outcomes.
For example, in the case of CF, potential genotypes of the offspring would be: two normal alleles (healthy non-carrier), one normal and one mutated allele (healthy carrier), or two mutated alleles (affects with CF). Conditions like sickle-cell anemia, Tay-Sachs disease, and phenylketonuria are also examples of autosomal recessive genetic illnesses, all requiring two copies of the recessive allele for the disorder to manifest.