Nick translation is a biological process in which a single-stranded DNA nick serves as the marker for DNA polymerase to excise and replace possibly damaged nucleotides. At the end of the segment that DNA polymerase acts on, DNA ligase must repair the final segment of DNA backbone in order to complete the repair process. In a lab setting, this can be used to introduce fluorescent or other tagged nucleotides by purposefully inducing site-specific, single-stranded nicks in DNA in vitro and then adding the nicked DNA to an environment rich in DNA polymerase and tagged nucleotide. The DNA polymerase then replaces the DNA nucleotides with the tagged ones, starting at the site of the single-stranded nick.