If we find life somewhere other than Earth, and attempt to sample its DNA, what will the different results mean?

All life on Earth uses DNA, because it all evolved from a common source and DNA does its job well in our environment. But different environments will almost certainly use different biochemistry. I would be quite surprised if alien life were found to use DNA--and if it did, that would be evidence that perhaps life here was "seeded" from elsewhere.

It wouldn't mean a thing. You have very different DNA than ants, what does it mean to you? It simply means you are two different species. However, if we find out alien life have very similar DNA to us, then that will be a much more interesting scenario to discuss.

1.  This would certainly be thought provoking, and I would want to see what parts of DNA are the same. I could be that there are some really common ways to do things, like cell membranes for instance, and those develop early and spread, and from the simple genomes there are really only a few ways for that to make sense. It could also mean that there was a common source. How that occurs would be thought provoking. It could be evidence of panspermia, where life was seeded on many planets from space. If its within the solar system, cross-contamination of some kind would seem likely. 2. It would indicate that life arose independantly in each case, and the chaos of early life took different paths. 3. It would mean that there are mutliple chemistries capable of supporting life, and our use of DNA is a coincidence. Or, different environments could lend themselves to different chemistries (by chemistries I mean something like organic chemistry, where there are a few key chemical reactions that build up complex structures, and as a consequence of this certain molecules and classes of molecules in use). Something based on silicon is often proposed.

Thank you for an excellent and subtle question. There are some excellent answers here, but I didn't see anyone mention the first thing that springs to my mind. If the extraterrestrial lifeform is somewhat similar to life on Earth[1], then what proteins and structures are coded for? It isn't often discussed, but over the history of the Earth,  lots and lots and lots of things have been lost. Entire orders, classes and phyla have been lost, along with many unique genes and the proteins they coded for. Except for clues in the fossil record, we don't know what has gone missing. This is often referred to in the context of "maybe some recent extinction has wiped out the cure for cancer". But the cure for cancer doesn't begin to describe what we might find. Perhaps there's a set of genes which give complex organisms effective immortality. Those genes might have been lost because immortal organisms had too few offspring, or perhaps couldn't deal with changing environmental conditions. Maybe there's a set of genes which lead to comprehensive and effective radiation damage repair. Such genes might allow us to explore space with impunity. Perhaps organisms with these genes died out because they stopped mutating. Maybe there's a set of genes which allow suspended animation of complex animals? Volitional birth control? Limb and organ regeneration? Parthenogenesis? Eliminates hypoxic cell death? Really, we don't know enough about biochemistry to know where the limits of the envelope lie. Anything we could learn about an extraterrestrial lifeform would be interesting and potentially very very useful. Great question, Best Rgds, -H- [1] Carbon based life with protein based structures.

The odds could be pretty high that if we find life elsewhere in this solar system, it would be DNA based. Why? We found several http://en.wikipedia.org/wiki/Martian_meteorite , meteorites that we found on Earth that were originally Mars rocks ejected by an impact. Life could had been originated here (or in another planet of this solar system) and small bacterias trapped in those meteorites could had bring life to other planets (or the same one, if what ejected that rock originally was big enough to end all life here). Could also be non-dna based life on other planets/moons too, or DNA based but with a different "alphabet" (several basic blocks are interpreted in the same way for all life here, something that don't need to happen for totally indepently developed DNA). But first we must find it, understand it as life, and analyze it. Regarding other solar systems, probably the trip could take too long to find around here "active" lifeforms coming from another star system. And going to another solar system could be outside our reach for what remains of our civilization.

1) Life, both on Earth and the alien world, has a common source 2) There is no common source OR both branched off from the common ancestor long, long ago ( like billions of years). 3) Life is more versatile and complex than we thought it would be. On Earth, RNA viruses have RNA which is made up of A,U,C,G instead of DNA which is A,T,C,G. There is a lot of research going on in artificial life with robots and computer programs mimicking the behaviour of living systems. It is possible that creatures in another world may have organs or cells with nuclei which are more like computer chips than terrestrial cells which contain genetic material.

If it has DNA at all, then either (a) DNA is the only comparably simple way for life to store its blueprints, or (b) that life shares a common ancestor with us, or (c) something is very wrong with our beliefs about the world.

Who is to say what is and isn't from this planet? The TARA expedition(s) have fished out more than 40 million new genes from the oceans ever since it began, in 2004 (?)  and 350,000 unknown species of life between 2009 and 2013. [I heard this from a documentary on BBC] More here: http://oceans.taraexpeditions.org/en/m/science/news/first-scientific-results-from-the-tara-oceans-expedition/ They also have an App.

There is no reason think this lifeform would have DNA, there could be a wide variety of molecules that are compatible with life. If we find an alien and it does use DNA as its basis for life then it is probably from contamination from Earth.