Fig. 2. Quantification of mitochondrial DNA copy number in heart ventricles of Antarctic notothenioids that vary in the expression of Hb and Mb. The mitochondrial-to-nuclear DNA ratio (mtDNA:nDNA) was quantified using qRT-PCR. The copy numbers of NADH dehydrogenase subunit 2 (ND2) and 16S ribosomal RNA (16S) were measured as indices of mtDNA copy number. Nuclear DNA copy number was quantified by measuring the copy number of citrate synthase (CS). Values were normalized to the mtDNA:nDNA ratio in N. coriiceps. Values are means ± s.e.m. (N=6).