1) A biological process consisting of chromosomal rearrangements and duplications. These phenotypes are often seen in the karyotype of cancer cells, where there is an imbalance between the mechanisms of cell-cycle control and mutation rates within aberrant genes. Ataxia telangiectasia is a disease that is resultant from mutations in the ATM gene, which is a cell cycle checkpoint gene. Nijmegen breakage syndrome is also a disease characterized by chromosomal and genomic instability.

2) An increased tendency of the genome to acquire mutations when various processes involved in maintaining and replicating the genome are dysfunctional.