Eukaryotic organisms differ dramatically in the amount of DNA found in each of their cells, a quantity termed an organism’s C-value (Table 8.4). Each cell of a fruit fly, for example, contains 35 times the amount of DNA found in a cell of the bacterium E. coli. In general, eukaryotic cells contain more DNA than prokaryotic cells do, but variation among eukaryotes in their C-values is huge. Human cells contain more than 10 times the amount of DNA found in Drosophila cells, whereas some salamander cells contain 20 times as much DNA as human cells. Clearly, these differences in C-value cannot be explained simply by differences in organismal complexity. So, what is all the extra DNA in eukaryotic cells doing? This question has been termed the C-value paradox. We do not yet have a complete answer to it, but analysis of eukaryotic DNA sequences has revealed variation in sequence complexity that is absent from prokaryotic DNA.