[philipov]

How do you propose to make pairs out of an odd number? Each nucleotide binds to only one other nucleotide.

[dnautics]

romesburg made 5 letter pairs, by allowing let's say a third one called "P" for no good reason, to do the following matches:

A:T T:A C:G G:C P:P

[sharpneli]

Nucleotide that binds only to itself.