Nuclear DNA content and genome size of trout and human.

NUCLEAR DNA CONTENT AND GENOME SIZE OF TROUT AND HUMAN In their recent paper, Thomas et al. (1) discussed design, resolution, sensitivity, and reproducibility of the National Aeronautics and Space Administration/American Cancer Society flow cytometer. The results of their study demonstrated high stability and sensitivity of the instrument, which is suitable for detection of near-diploid tumor cells. Although the performance of the instrument is impressive, we believe that Thomas et al. made serious errors in calculating the DNA contents of trout and human. To estimate the DNA content of human cells in picograms of DNA, the authors used trout red blood cell nuclei as the internal reference standard and assumed 2.37 pg of DNA for a trout nucleus. With this value, the DNA contents of human female and male nuclei were estimated to be equal to 3.77 and 3.70 pg of DNA, respectively. The new estimates for trout and human differ drastically from previous ones, which range from 4.9 to 6.3 pg for various species of trout (2–5) and from 6.0 to 7.0 pg for human (5–9). Because trout and human nuclei are often used as internal reference standards to determine genome size in animals and plants (5,10,11), the results published by Thomas et al. (1) need correction to avoid serious mistakes. Careful reading of the paper showed that the DNA content of trout (the authors did not specify the species) was derived after determining the ratio of mean DNA content of human male to trout to be 1.565. The DNA amount of the human nucleus, 3.70 pg, was calculated with the assumption that there are 6.162 10 nucleotides for the human male nucleus and that a mean nucleotide molecular weight of 360 g/mol. We believe these data are not correct.