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Cambridge Reference Sequence

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The Cambridge Reference Sequence (CRS) for human mitochondrial DNA was first published in 1981[1] leading to the initiation of the human genome project. The abbreviation "CRS" is also sometimes used to mean "coding region sequence".

A group under Dr. Fred Sanger at Cambridge University sequenced the mitochondrial genome of one individual of European descent during the 1970s, determining it to have a length of about 16,569 base pairs (0.0006% of the total human genome) containing some 37 genes.

When other researchers repeated the sequencing, some striking discrepancies were noted. The original published sequence included eleven errors, including one extra base pair in position 3107, and incorrect assignments of single base pairs. Some of these were the result of contamination with bovine and HeLa specimens. The corrected revised CRS mtDNA was published by Richard Andrews in 1999.[2] The original nucleotide numbering was retained to avoid confusion. The reference sequence belongs to European haplogroup H2a2a1. The revised CRS is designated as rCRS.

When mitochondrial DNA testing is used for genealogical purposes, the results are usually reported as differences from the revised CRS. Such differences are not necessarily mutations: the CRS is a reference sequence rather than a record of the earliest human mtDNA. A difference between a tested sample and the CRS may have arisen in the lineage of the CRS or in the lineage of the tested sample.

Further reading

  • Roe, BA. Frederick Sanger (1918-2013). Genome Research 2014: 24: xi-xii. The tribute includes an account of Sanger's work on the Cambridge Reference Sequence.


  1. S. Anderson et al., "Sequence and organization of the human mitochondrial genome, Nature, Vol. 290, 9 April 1981. pp. 457-465.
  2. Richard M. Andrews et al., "Reanalysis and revision of the Cambridge reference sequence for human mitochondrial DNA", Nature Genetics, 23, 147, 1999.

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