Introduction to ancient DNA
In tracing relationships through genetics, researchers have focused on mitochondrial DNA (mtDNA), which is passed from mother to child, and Y-DNA, which is passed from father to son. Such studies of ancient DNA in Europe and related remains in Asia are shown in table 1. Remains from North Africa and the Canary Islands are listed in table 2. Where Y-DNA haplotypes are included in a study, the STR numbers appear in table 3.
Notation for DNA:
G = guanine
A= adenine
T= thymine
C= cytosine
R = purine (adenine or guanine)
Y = pyrimidine (thymine or cytosine)
★☆Warning!☆★
The results of pioneer studies of ancient DNA may be unreliable for several reasons:
- The possibility of contamination with the DNA of people who had handled the bones is a major problem, which bedevilled early studies. Studies which sequenced DNA direct, without initial cloning, did not use stringent means to prevent contamination and/or did not check the DNA of all persons known to have had contact with the material may be marked in the tables as unreliable.
- Early studies mainly tested only a limited section of hypervariable region 1 (HVRI) of mtDNA. This excludes many of the markers used today, so that the haplogroup in some cases cannot be securely assigned to a present haplogropup.
- MtDNA haplogroups are assigned by means of their differences from the Cambridge Reference Sequence (CRS), which is now known to be H2a2. Therefore if no differences appeared, the result will be shown as CRS (or rCRS for revised CRS) with no other indicators. This was generally assumed to be haplogroup H by pioneer researchers. But CRS in HVR1 can also appear in U or HV. Where no differences were detected in a fragmentary sequence of DNA retrieved, it is more realistic to count it as a non-result.
More problems
- Y-DNA being more difficult to obtain from ancient remains, it is only comparatively recently that studies of ancient DNA have been able to include it. Richard Stevens has created an online map of the locations of sites of Y-DNA from ancient European DNA prior to 1000 BC.
- Nomenclature of haplogroups is being constantly revised, as new SNPs are discovered. Therefore the haplogroups assigned by the authors of even recent studies may need revision by the time of publication. Some attempt has been made in table 1 to update nomenclature, but for current haplogroup trees, with the markers that distinguish each haplogroup and sub-clade, see ISOGG's Y-DNA Haplogroup Tree and PhyloTree's mtDNA tree.
Genes for pigmentation, lactose tolerance and HIV resistance
- Some studies of ancient mtDNA or Y-DNA also include genes for pigmentation, as shown in table 1.
- Findings of the most common allele in Europeans associated with lactose tolerance (ability to drink raw milk without discomfort) in ancient DNA are listed in table 4.
- Findings of a mutation conferring HIV resistance in ancient DNA are listed in table 5 .