How well do we understand DNA?

The amount of DNA per cell is highly correlated with the cell volume of the species.This fact favors either a "skeletal DNA" explanation (sheer bulk of DNA has some function, but not any "complex" sequence-specific function), or a "pure junk" explanation (for large cells, DNA replication costs are trivial compared to other biochemical processes).The fact that the amount of DNA can vary widely even between two closely related species, and that large chunks of DNA can be deleted in some organisms without apparent ill-effect, strongly indicates that some DNA really is junk.See http://www.evowiki.org/index.php/Junk_DNA for graphics and references.