||p.3 right column 2nd paragraph:"The number of mitochondrial genomes per focus was calculated after measuring the number of mitochondrial genomes per cell, the total mitochondrial length, and the number of foci per unit length of mitochondria (Table 1). While the first two can be estimated reasonably accurately, it is difficult to be sure that all foci are detected. Therefore [investigators] used various approaches, reasoning that if different methods with different thresholds of detection gave similar results, one estimate would lend credibility to another (Table 1, line 6). The data were analyzed as follows: (i) immunolabelling with both anti-DNA and anti-BrdU (after growth in BrdU to substitute DNA fully) gave similar results (that is, ~7 genomes/focus) (ii) the average intensity of foci in images like that in Figure 1D had an intensity 9.2× higher than the weakest (Figure1F, legend) if the faintest focus then contains one genome, the average would contain ~9 (iii) foci had a diameter of ~68 nm (Table 1, line 4), sufficient to accommodate ~6 genomes packed as tightly as in the bacterial nucleoid [primary source 26] and (iv) analysis of replication rates are consistent with each focus containing ~10 genomes (below). Taken together, these results suggest the average focus contains 6–10 genomes, again consistent with earlier results [refs 18,19]."