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.
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