Bad DNA
 
Unnatural DNA structures presented at major science museums

 
 

Photo of good DNA, from University of Cambridge

First, here is a good DNA structure from the University of Cambridge. Note that there are two grooves spiralling down the length of the molecule. These are like the grooves running down braided hair, except that one is wide (the major groove), and the other is narrow (the minor groove). Also note that there are 10.5 base pairs per helical turn (the base pairs contain blue nitrogen atoms).

 
 

Photo of bad DNA from the Natural History Museum, London

Now some bad DNA from the Natural History Museum, London. This picture is from the Human Biology Gallery, genetics section, and was taken in May 2010. If it looks too neat, that's because it is. This bad DNA has 8 base pairs per helical turn and the major and minor grooves are identical.
 

 
 

Photo of bad DNA from the website of the Science Museum, London

This one is from the Science Museum, London. It is pretty close for the number of base pairs per helical turn, but the major and minor grooves are identical. Also, there is a giant-sized base labelled 'Nitrogenous base', which appears to span the entire gap between the helix backbones. It should be two bases paired together, as shown for all the others in this cartoon.