Skeletal DNA and the evolution of genome size.

The mass of DNA in a haploid nucleus is usually constant in any one species and is known as its C-value (134) or genome size. Just as atomic theory explains the different masses and properties of atoms, so genetics ought to be able to explain the different masses and properties of genomes. But despite elegant physical explanations for qualitative genetic variation and inheritance, in terms of how nucleotide sequences code for proteins, we lack a generally accepted theory of what determines genome sizes. Particularly puzzling has been the almost 105-fold variation in C-value among different eukaryote species (Figure 1). Often dubbed the C-value paradox (21,27, 137), it appears inexplicable in terms of qualita­ tive differences between organisms. The purpose of this review is to discuss recent ideas and evidence concerning the C-value paradox; these suggest that DNA may have quantitative noncoding functions (10, 11,27, 35) in addition to its better established qualitative coding ones. The problem is distinctly biophysical, involving the approaches and ideas of both Galileo and Darwin; i.e. Galileo's principle of scaling and Darwin's principle of selection. Galileo (54) first showed that mere