g. individual, population, etc.), nucleotide state stability/mutability (that may be sequence context dependent), and
genetic drift. These factors, alone and in combination, have been previously Dabrafenib mouse suggested to explain the difference between phylogenetic and pedigree substitution rates in the CR ,  and , departures from the correlation between observed relative substitution and heteroplasmy rates by position in the CR ,  and  and patterns of substitution (, ,  and , among others) and heteroplasmy  and  in the coding region. In a substantial departure from the above-mentioned studies regarding heteroplasmy across the mtGenome, a very recent examination of mtDNA sequences from 1085 individuals using high coverage depth MPS data and an ∼1% heteroplasmy detection threshold found 4342 total PHPs at 2531 mtDNA positions (of 13,659 positions examined), of which only 69.42% were observed in just a single individual . Relying on the same relative
substitution rates published by Soares et al.  referenced above, Ye et al.  reported a positive correlation between relative substitution rates and heteroplasmy rates (R2 = 0.3702). However, coding region heteroplasmies were not separated from CR heteroplasmies for that analysis, and an association between substitution and heteroplasmy hotspots has been previously described for the CR . When we applied the same analysis to all 166 PHPs detected in our study (64 and 102 selleck chemical PHPs in the CR and coding region, respectively), a similar positive correlation was observed (R2 = 0.3003, r = 0.5480; see Fig. S6a) despite the clear lack of correlation between relative substitution rates and heteroplasmy rates among Histidine ammonia-lyase the coding region PHPs in this study. When the same regression
analysis was performed using only the 3547 coding region PHPs reported by Ye et al. , a much weaker positive correlation between relative substitution rates and heteroplasmy rates was observed (R2 = 0.1076, r = 0.3280; see Fig. S6b). Additionally, further examination of the PHPs reported by Ye et al.  indicated that some may be due to mixtures between distinct individuals/samples, rather than true intraindividual mtDNA variation . For example, among the 71 PHPs reported for sample HG00740, nearly all of the positions are diagnostic for two distinct mtDNA haplogroups (L1b1a1a and B2b3a; according to Build 16 of PhyloTree ). Similar issues were observed among the PHPs described in another recent report on human mtGenome heteroplasmy . In that paper, nearly all of the 20 PHPs given for sample NA12248 (for example) can be ascribed to one of two haplogroups (U5b2a2b or H1e), and few PHPs that would be expected from a mixture of two samples representing those haplogroups are absent. These findings cast some doubt on the veracity of the incidence and pattern of heteroplasmy reported in the Ye et al.  and Sosa et al.