Final answer:
To determine if a mutation is autosomal recessive, analyze a pedigree for rare occurrences of a disorder, equal gender distribution, and absence in parents but presence in siblings, indicating carrier status. Autosomal recessive traits require two copies of the recessive allele to be expressed.
Step-by-step explanation:
To determine if a mutation is autosomal recessive from a pedigree analysis, we need to examine how the trait is passed down through generations. Looking at a pedigree chart, if the disorder appears relatively rarely, and both sexes are affected equally, this can indicate that the condition follows an autosomal recessive pattern. When two individuals show the disorder on the chart and they are siblings, but their parents do not show the disorder, it suggests that the parents are likely carriers. Carriers are heterozygous, meaning they have one copy of the recessive allele and one copy of the normal allele.
Additionally, if the disorder does appear, according to Punnett square calculations, there is typically a 25% chance that any child they produce will express the disorder. This is because two carrier parents have a 25% chance to pass both of their recessive alleles to an offspring. It's important to note that, unlike autosomal dominant traits, individuals with autosomal recessive disorders are homozygous for the trait—they possess two copies of the recessive allele.
Conclusively, analyzing a pedigree allows the identification of autosomal recessive traits through the patterns of unaffected carriers producing affected offspring, equal gender distribution, and the absence of the trait in consecutive generations, which might appear again when two carriers mate.