QUESTION: 
Regarding DNA, 20 acids exist for all life forms on Earth! Does this mean
that life on Mars or anywhere else would use DNA?

ANSWER from Jack Farmer on November 20, 1996: 
We really don't know the answer to your question because we only have one
example of life so far, namely that here on Earth. We use that as a model,
but many of us leave the door open for life to have developed differently
on Mars. It would not necessarily have to be DNA-based; it just needs to
carry out basic encoding functions and be able to self-replicate. It is
probably fair to say it should be DNA-like, a long chained polymer of
carbon and other biogenic elements.