DNA Complement Fun

You’re probably familiar with the DNA bases A, C, G, T and how A is the complement of T and C is the complement of G, and vice versa.

A neat mental exercise is to find the complement of the degenerate bases like R which represents both A and G.

Suppose the complement of R is a base that represents the complement of A and the complement of G. The complement of A is T and the complement of G is C, so the complement of R is Y (a degenerate base that represents T and G).

Here’s a whole list of them. Try it out.

It’s fun to think of complement as an function.

You see neat patterns like, every degenerate has exactly one complement, so complement is a bijective function. The fixed points of complement are at S (represents C and G), W (represents A and T), and N (represents all the bases A, C, G, and T). In fact, there will always fixed points at degenerate bases that represent a even number of bases. This is true even if we expand out the original A, C, G, T to fictional bases like Q and Z (I made Q and Z up).