I made each sugar-phosphate twistie with 10 stitches on two 3mm circulars. One one side you just knit, and on the other side you increase at the one edge and decrease at the other. I wasn't convinced it was twisting for quite a while, but it works...
Then I put them together with my DPN-skewered base pairs, which were 6-stitch icords (11 rows) with the ladder crocheted up, and awkwardly tacked them on. Awkward, because it was as hard to hold as a cactus ;)
You can stretch it out, though the twistiness rebels and springs right back...
Sorry for the color-leeching. I'd already said on Rav that the base pair colors matched Baby Three's cotton singlets, and baby's gender is still a secret.
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Meanwhile, here are my two actual contributions to the DNA-pool, KO'd yesterday after running around with Grandma. Filthy, but cute Ü. Don't you just love kids a tiny bit more when they're asleep? hehe.