Final answer:
Autosomal recessive inheritance involves conditions caused by recessive alleles on autosomal chromosomes, with cystic fibrosis as a primary example, and includes other disorders like sickle-cell anemia and Tay-Sachs disease.
Step-by-step explanation:
Conditions associated with MR, now more commonly referred to as Intellectual Disability, that have an autosomal recessive inheritance pattern, relate to conditions inherited when both parents carry a recessive allele of a gene on one of the 22 autosomal chromosomes. An example of such a condition is cystic fibrosis (CF), in which children have a thick mucus accumulation in the lungs and digestive tract, making breathing difficult. Carriers of an autosomal recessive disorder do not usually show symptoms but may pass the recessive gene to their offspring. The chance of two carriers having a child with the disorder is 25%, reflecting the classic 3:1 Mendelian ratio for dominant to recessive inheritance. Other examples of autosomal recessive conditions include sickle-cell anemia, Tay-Sachs disease, and phenylketonuria. These disorders require a child to inherit two copies of the recessive allele to express the condition. The likelihood of inheritance is illustrated by a Punnett square, demonstrating the probabilities of each potential genotype and phenotype.