It can be done chemically without a template or polymerase. Oligonucleotide synthesizers (that make primers for PCR) do make single stranded DNA, base by base, chemically. These oligonucleotides can be made quite long these days, and then annealed to make double stranded DNA.
Hello Levi, duplication of DNA is via DNA pols and RNA is via Reverse transcriptase. For RNA viruses, RNA is the only genetic material.. once it enters the host the RNA is reverse transcribed to the DNA via the Reverse transcriptase and then the DNA is multiplied via DNA pols to give back the viral RNA..
Technically to answer ur question. Yes possible via PCR and RTPCR.
Whether DNA/RNA can multiply on its own is not possible.. atleast we haven't found such as process yet ;)
There are viruses without DNA-stage in life cycle. Such viruses use RNA-dependent RNA-polymerase. So, it's one more way for duplicate RNA, but I havn't heard about it usage in in vitro experiments