Making Sense of Animal Genome Size Standards Measured by Flow Cytometry
Mentor:Thomas Vandergon, Professor of Biology, Pepperdine University
Genome size is defined as the DNA content in one set of chromosomes reported as the C-value in pictograms (pg). Genome size analysis can provide critical information for comparing evolutionary, species, and population relationships. Currently, animal C-values ranging from 0.02 to 132.83pg are available for approximately 5000 species, but a majority of animal C-values remain unmeasured. C-value variation may reflect environmental influence, evolutionary history, ploidy level, and cell or body size. Currently C-value variation does not correlate reliably to most of these hypothesized factors. This may be due to scarce data, however, a confounding problem is that different genome size studies often report different results even for the same species! Why would that be? Two sources of variation or error are probable; 1) the technique used, and 2) the dependence upon a “known” standard animal C-value to determine an unknown C-value. Currently, about a dozen animals are used as standards for genome size analysis. Unfortunately, for the common technique known as Flow Cytometry (FCM), the genome sizes of these “standards” do not correlate, meaning that C-values based on different standards are not the same. It is difficult to rely on reported data when standard values are not reproducible. The goal of this study is to identify a small set of common, reliable animals to use for genome size standard correlation using FCM. For FCM we isolate nuclei from blood or tissue in PBS containing 0.1% Triton X-100, stain with propidium iodide and then measure fluorescence on a Quanta SC-MPL system. We measured nuclei from cow, goldfish, zebrafish, Drosophila, and chicken. Of these, only two matched reported C-values (Drosophila, 0.18pg and chicken, 1.25pg), and cross correlate in FCM. We continue work toward finding additional animal standards that cross correlate to Drosophila and chicken, thus forming a globally useful standard C-value set.