Practice question

Mitochondrial cells contain many copies of mtDNA molecules that can be heterogeneous within same cell, condition termed heteroplasmy. During mitotic segregation, mutant and wild-type mitochondria distribute randomly to daughter cells, generating offspring cells with varying proportions of mutant mtDNA. Phenotype severity often correlates with percentage mutant load and tissue energy demand, leading to variable expressivity even within same family sharing same mutation. Autosomal, X-linked, and Y-linked traits lack heteroplasmy because nuclear genome exists as diploid pair. Hence variable expression due to heteroplasmy characteristically describes mitochondrial inheritance.