Beaded DNA: Groove and Twist

After watching my video on beaded DNA , Cindy Holsclaw (beadorigami) sent me this link on DNA's B Form, A Form and Z Form.  From there, I learned that the DNA design in my video has just about the right amount of twist.  In particular, my base-pairs-per-turn ratio came to the same as the B-DNA structure.  This was a lucky accident.  In real DNA, the two helices are not equally spaced on both sides; in other words, DNA has both major and minor grooves.  One of my earlier samples was just like that, in fact.

I thought it was an error, so I "fixed" it for the video, but now I thought I’d show it to you.

What causes the unequal spacing in this beaded double helix is more (or longer) beads on the edge.  In other words, make it ruffle more without changing the first steps to make the ladder.  I wonder if there is a similar cause for the unequal grooves with DNA molecules.  Wouldn't that be cool if art explains nature.  Here's what it looks like when I tried to untwist it, a ruffly colorful mess.

Click the photos to buy it.  It's the only one.