Dark Lord Prime: Too bad viruses don't have DNA.
Well, some do. Viruses are substantially more different one from another than other animals are. Since they don't have their own cellular machinery they can very plausibly inject themselves into the host cellular machinery at many different points. As such we recognize seven types of viruses that each have a different central dogma of their molecular biology.
Type I use double stranded DNA just like humans, monitor lizards, and bananas.
Type II use single stranded DNA. Which is basically an entirely different method of doing life where you copy your DNA from the RNA copies that you make rather than from the original DNA.
Type III don't use DNA at all but double stranded RNA instead. This is another entirely different method of life that animals plants and fungi don't use.
Type IV and Type V viruses both just use single stranded RNA, but they differ in that they actually get read in the opposite direction, meaning that their codes don't mean the same thing and aren't interchangeable.
Type VI and VII viruses reverse transcribe themselves into DNA that is injected into the host's DNA system. They differ in what kind of molecule they use to template that reverse transcription (RNA or DNA).
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All macroscopic and almost all microscopic life in the world today is basically like Type I viruses. But life is clearly possible with all seven techniques. When we go to other stars, there is no reason to believe that the life we find there will even use DNA. It could be based on single stranded RNA or something. Because we have some life that works like that right here and right now.
But viruses run the full gamut of possibilities for nucleic acid based lifeforms. And some of them do use the same kind of DNA that we do.
-Frank
