Fig. 2. Proportions of cellular DNAs during development. Changes in the relative proportions of the chromosomal DNA, mitochondrial DNA (mtDNA) and the extrachromosomal ribosomal DNA (rDNA) were estimated by quantification on pulsed field gels. (A) High molecular weight DNAs were separated by pulsed field gel electrophoresis and stained with ethidium bromide. The three DNA species were quantified by digital image analysis using several different exposures. Phosphoimager analyses of Southern hybridizations were used to correct for the proportion of each DNA trapped in the wells. The signal obtained for mtDNA is shown as an example (B). (C) Changes in the proportions of mtDNA, rDNA and chromosomal DNA are shown for a representative experiment. Note that their proportions do not change during the time cells undergo mitosis (indicated by the bracket). (D) The measured peak values for flow cytometry DNA profiles of mononucleated cells are plotted for the same population of cells described in C (filled circles). The expected peak values were calculated from the proportions of the different DNA species in C and assuming that all cells at 6 hours are in G2 and that all cells that divided later remained in G1 (open circles), or progressed through an S phase and arrested in G2 (open squares).