A slippage event normally occurs when a sequence of repetitive nucleotides (tandem repeats) are found at the site of replication. Tandem repeats are unstable regions of the genome where frequent insertions and deletions of nucleotides can take place, resulting in genome rearrangements.
During replication, a slippage event often happens when tandem repeat sequences are located at specific sites. These repetitive regions within the genome frequently undergo insertions and deletions of nucleotides, resulting in changes to the overall genomic structure.