The "C-Value Paradox"


    This chart shows the range of C-value [genome size, measured as number of Kbp of DNA] for a variety of organisms. So-called "simple" prokaryotic organisms in general have less DNA per genome than do more "complex," eukaryotic organisms, such as plants and animals. The so-called C-Value Paradox refers to the observation that genome size does not uniformly increase with respect to perceived complexity of organisms, for example vertebrate with respect to invertebrate animals, or "lower" versus "higher" vertebrate animals (red box). Note for examples that some Amphibians have more than 10-fold more DNA than do Mammals, including humans.

    There is in fact no "paradox." Evolution does not proceed in a linear manner, nor is there a linear succession of organisms from "lower" to "higher." Despite differences in DNA content, the number of genes in any vertebrate genome is roughly similar. Also, plant and amphibian genomes in particular are frequently polyploid, in which the chromosome number undergoes doubling to two-, four, or eight-fold. without a radical change to the form of the organisms.


Figure © 2005 Griffiths et al.; All text material © 2011 by Steven M. Carr