PNA is the Pernese genetic material.
PNA is composed of three strands in a triple helix. As in Terran DNA, one strand contains the genetic code for the organism. Both the second and third strands are complementary and used in replication.
There are seven Pernese bases, but only three are used in the actual genetic code, A, B, and C. The two complementary strands consist of the bases A', B', C', and N. A' is the base that binds with A, B' with B, and C' with C. The N, or "Null", base binds with all three of these pairs. It is only used to complete the base triad and is not read during replication. The complementary strands mirror the main strand alternately, so every other base in each one is N, and both must be read for replication.
Like Terran DNA, PNA is read in codons of three bases. This means that there are 27 possible codons. Two codons indicate to start reading to produce a protein, and two indicate to stop reading. The remaining 23 all code for an amino acid.
The structure of PNA makes it harder to split, which makes mutations much less likely. Most mutations are immediately fatal. Only three Pernese mutants are known: a symbiotic microorganism in fire lizards that mutated into a parasite, and two albinos, a dragon, Ruth, and a fire lizard (the fire lizard functions as a sort of cursor in the game Dragon Riders: Chronicles of Pern, and may be non-canon). Ruth would have died as well if his egg hadn't been broken by Jaxom.
The low mutation rate also means that pathogens are extremely rare. In the unlikely event that an infectious pathogen is mutated from a microorganism, it will wipe out its host population completely and die out itself. Pernese organisms, since they almost never have to deal with diseases, are incapable of developing immunities. The only known case of immunizing Pernese organisms, ending the Dragon Plague of the Third Pass, involved altering their genetic code so the pathogen couldn't affect it.
Drum codes are based on PNA codons. One of the "Start" codons, for example, is the "Attention" sequence for drum messages.