From the moment life gained a foothold on Earth the diversity of organisms has been written in a DNA code of 4 letters. The latest study moves life beyond G, T, C and A and introduces 2 new letters of life: X and Y.

and here’s P and Z:

Researchers have shown that 2 synthetic nucleotides called P and Z fit seamlessly into DNA’s helical structure, maintaining the natural shape of DNA. Moreover, DNA sequences incorporating these letters can evolve just like traditional DNA, a first for an expanded genetic alphabet. The new nucleotides even outperform their natural counterparts. When challenged to evolve a segment that selectively binds to cancer cells, DNA sequences using P and Z did better than those without.

more on Z and other noncanonical bases:

Z and other modified DNA bases seem to have evolved to help viruses evade the defenses with which bacteria degrade foreign genetic material. The eternal arms race between bacteriophages and their host cells probably provides enough selection pressure to affect something as seemingly “sacrosanct” as DNA. “Right now, everyone thinks the modifications are just protecting the DNA. People almost trivialize it.” But something more may be at work: The triple bond of Z might add to DNA’s stability and rigidity, and perhaps influence some of its other physical properties. Those changes could carry advantages beyond hiding from bacterial defenses and could make such modifications more broadly significant. After all, no one really knows how many viruses may have played with their DNA like this. “Standard genome sequencing methods for looking for biological diversity in nature would fail to find these, because we are looking in a way that assumes a common biochemistry that is not present.”

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