Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.
Person Condition Percent Mitochondria with
Mutation
Proband A and PN >90%
Brother A and PN >90%
Brother Asymptomatic 17%
Mother PN 86%
Maternal uncle PN 85%
Maternal cousin A and PN 90%
Maternal cousin A and PN 91%
Maternal Asymptomatic 56%
grandmother
In what way does a condition caused by mtDNA differ in expression and transmission from a mutation that causes albinism?
2. Mendel's Laws of Inheritance
Pedigrees