COI sequence variability
A growing number of studies have shown that COI sequence variability is very low and that the COI sequences of even closely related species differ by several percent, making it possible to identify species with high confidence. This region is 648 nucleotide base pairs long in most groups and is flanked by regions of conserved sequences, making it relatively easy to isolate and analyze. The “Folmer region” at the 5′ end of the cytochrome mobile barcode scanner mitochondrial region is emerging as the standard barcode region for almost all groups of higher animals. DNA barcode sequences are very short relative to the entire genome and they can be obtained reasonably quickly and cheaply.