Kimberly Chapman has posted a neat guide to knitting your own model of the Double Helix. Scroll to the bottom of the page for the instructions. From her guide:
This is a knitted model of DNA, complete with GC/TA base pairs represented by orange-green bars with a pointed join and blue-yellow bars with a stepped join (because there weren't enough stitches to make a wave or curve), replicating the standard simplified DNA model. As you can see from the pictures, it also makes a good toy insofar as it holds its shape while squished or stretched, because it is stuffed firmly with cotton balls.
Link (via MAKE: Blog)
UPDATE: Thanks to all the readers who pointed out that real DNA, unlike the yarn model, twists to the right like a regular screw. Link
