Final answer:
Traits with autosomal recessive inheritance usually result from a loss of function mutation, where individuals must inherit two recessive alleles to express the trait, while carriers with one recessive and one normal allele do not show symptoms.
Step-by-step explanation:
Most traits that exhibit an autosomal recessive pattern of inheritance are the result of a loss of function mutation. This type of mutation leads to the nonproduction or the production of a nonfunctional version of a protein, and these nonfunctional alleles are typically recessive to functional alleles. To express a recessive trait, an individual must inherit two copies of the recessive allele – one from each parent.
Individuals with just one copy of the mutant allele and one copy of the wild-type allele do not usually exhibit the trait and are known as carriers. The wild-type allele can sufficiently cover for the loss of function of the nonfunctional allele, which means the phenotype of autosomal recessive disorders does not manifest in heterozygous individuals.