The revised Cambridge sequence, commonly used as a reference for human mtDNA, contains a placeholder at position 3107 added to correct a sequencing error and to preserve the established position numbers. This placeholder is not used internally within the CMEM Web database, and results displayed on MITOMAP and MITOMASTER are adjusted to the standard numbering scheme as they are returned. However, if you are querying the database using SQL queries, as described in CMEM Web Cloud Interface, then you will have to make these adjustments yourself (most easily done with the revised_position database function.

Because of this placeholder, it is impossible, using the standard numbering scheme, to have a human mtDNA variant for position 3107. Texts commonly list the human sequence as 16,569 bases in length, but this includes the placeholder, so only 16,568 nucleotides (numbered 1 to 16,568) are stored internally for the human reference sequence.