Variable penetrance of mitochondrial mutations

(a) (b) Homoplasmic segregation Primordial germ cell Primary oocytes Mature oocytes 100% containing wild-type ii mutant and mutant mitochondria ’ " Low proportion of mutant Mitochondria mitochondria Mutant Wild-type (unaffected individual) \a is 100% 100%100% 100%100% {All progeny homoplasmic. ‘Wfimwmi ********** Intermediate Heteroplasmic segregation (mildly affected indIVIduaI) 50% mutant Motherscells with a low proportion of . High 10% 100% 50% 70% 30% _ mutant m'tochondna- (affected individual) 1 Each progeny_ may W Restriction in i fWAheteroplasmic female W ‘ differ depending on mitochondrial i x Q can thus produce eggs i replicative segregation number occurs early i Mitochondrial with a greater or lesser i during egg production j in egg production 1 number amplified ‘ proportion of mutant WWW, W , 1 (a bOttIEHECk Effed>- as oocytes mature. _ mitochondria.