It looks like complex DNA structures came partly as a response to DNA damage. I think maybe we can make mutations occur in single cells or viruses anytime, not just during reproduction. Then if the cell has mechanisms in place to repair damage it can.
Here's a good table of effects:
1. Ionizing radiation - two strand breaks in DNA - causes deletions and translocations
2. UV light - pyrimidine dimers - errors in nucleotide choice during repair (this could be as simple as chaning some of the tipo or value data of a DNA entry (you have to know how DNA reads in the program to understand that)).
3. Chemicals - Base analogue mispairing - single nucleotide substitution (same as above basically I think)
4. Spontaneous - isomerization of a base - single nucleotide substituition.
-------------------- or slipped mispairing - framshift and short deletion
5. Transposition - insertion of transposon into gene - insertional inactivation
6. Mispairing of repeated sequences - unequal crossing-over- deletions, addition, inversions
7. Homologue pairing - gene conversion - single nucleotide substitution.
Don't ask me what they all do, I don't know. I'm just copying from my bio book. Things like reproduction tend to increase the probability of mutations I think. Dunno.