There are two makerbottable versions, the "Left-handed" and "Right-Handed" spirals. Right-handed corresponds to native B-DNA, the active form in most cells, and Left-handed corresponds to Z-DNA, the generally inactive form. Both are technically inaccurate with regard to spiral winding, but that's easy to fix in the script if you have a machine capable of supported printing. See here for information on accurate structure:
en.wikipedia.org/wiki/Z-DNA#Comparison_Geometries_of_Some_DNA_Forms
There is a third model representing "B-DNA" as accurately as I was willing to spend time on. :)

There's a fair amount of cleanup to do, thanks to the first layer or two of each base pair being dropped into thin air. Better skeinforging might lead to better models. A firmly supported build platform would help too, which I lacked in printing mine.

Note: The OpenSCAD file contains support for cuboidal bases and ovoid backbones, as well as options to vary the spacing between strands and their relative rotation from one another. And how twisty they are. And how densely to pack in the bases. Basically the works, it's OpenSCAD after all.

IMPORTANT: After you have printed, remember to post under "I made one!" on Thingiverse. If you don't, you'll develop nasty boils and members of whatever gender you are into will shun you.