Double Stranded Breaks
Caused by radiation, freezing, viruses
Usually fatal if unrepaired. Stops cell division.
Repair mechanisms find loose ends and join them.
When there are multiple breaks, the wrong ends can be joined, leading to inversions and deletions and chromosome fusions.
Repair frequently ends up duplicating 3 or 4 bases at join.
Repair mechanisms can be guided by homology in polyploid organisms. Sometimes this induces large scale duplication.