Y-DNAThis part of the Danish Demes DNA project is based on STR (short tandem repeat) testing of the male Y-chromosome.
Test results consist of numbers which represent the counts of the number of times a "junk" (non-functional) DNA segment is duplicated at a given marker (location on the chromosome).
At FamilyTreeDNA, five levels of Y-chromosome STR testing are offered to group members: 12-, 25-, 37-, 67-, and 111-marker tests (every level of testing tells you something,
but most project members will find themselves ultimately wanting to test at least 67 markers).
Collectively, the pattern of numbers resulting from STR testing is called a person's haplotype (sometimes called a "motif").
The Y-chromosome is possessed only by males and is passed on only from father to son, so only males can be tested for this part of the project.
STR testing measures relationship in a time frame of hundreds_of years, making the distance to the MRCA (most recent common ancestor) sufficiently close to be genealogically useful.
And "useful" is an understatement. STR testing is a powerful tool for determining whether people can or cannot have shared a recent common ancestor.
There is another form of Y-chromosome DNA testing called SNP testing (the acronym stands for "single nucleotide polymorphism" and is pronounced as a single word, "snip").
Results of SNP testing are expressed as + or - (positive or negative) to indicate the presence or absence of a particular mutation.
Each suspected mutation requires a separate test, which is one reason SNP testing can become more expensive than STR testing.
The haplogroup is a measure of deep ancestry. The MRCA may be thousands of years in the past, which places the individual's ancestry in a paleoanthropological time frame.
Haplogroup determination is of practical use for the project because it broadly defines and separates the most distinct family groups; that is,
families with no prospect whatsoever of a connection in "genealogical time," making it a useful way to divide up the project.
For the individual, knowing one's SNP subclade greatly enhances one's appreciation of history because the literature on the genetic history of humanity,
correlated with historic and pre-historic events, is growing rapidly. Over the last decade, SNP testing has become increasingly refined as more SNPs are discovered,
to the extent that it is reaching down into "genealogical time." For this reason, I recommend members keep themselves
deep SNP tested to the currently available extent, in anticipation of this refinement.
Having two different tools approaching the same question makes for very strong conclusions about your ancestry.
mtDNA
This part of the Danish Demes DNA project is based on the test results of sequencing regions on one's mitochondrial DNA (mtDNA).
Mitochondria occur in the cells of all humans, regardless of gender, so both males and females can have their mtDNA tested.
The results of such a test can place someone in their "mtDNA haplogroup" (not to be confused with, for males only, their Y-DNA haplogroup).
Mitochondria are passed on by, and only by, one's mother, so mtDNA is useful only in characterising your most distant ancestor on your matrilineal (direct female) line.The mitochondria in our cells perform the critical function of metabolism, using oxygen to burn fuel to supply us with energy.
We would quickly die without them (e.g., cyanide acts by disabling them), so nature doesn't tinker much with these genes.
But there are two sections of the mtDNA strand that appear to have no function, so these sections are subject to retained mutations.
These sections are known as "hypervariable regions" and are named HVR1 and HVR2. Without the two hypervariable regions, there wouldn't be enough mutation in the mtDNA
molecule to be of much use in sleuthing out our ancestry. As it is, even the hypervariable regions do not mutate frequently enough to be of use in short term
(i.e., genealogical) time frames. The mutations are extremely useful, however, in revealing our deep ancestry in a paleoanthropological time frame.
The first individual to have their mtDNA sequenced had it done experimentally in 1981, and their sequence has arbitrarily been made the standard against which all other mtDNA sequences are now compared.
This standard is called the "Cambridge Reference Sequence" (CRS); and, today, mtDNA test results are expressed as differences from the CRS.
Fortuitously, the CRS is also the most common mtDNA sequence in Europe (which, if you think about it, was statistically the most likely one to have been randomly
chosen among the scientists in a laboratory in western Europe). And while the CRS is the most common mtDNA sequence in western Europe,
it is not the most ancestral one that has since been determined. In a hierarchical (evolutionary) "tree" of mtDNA haplogroups,
the CRS turns out to be Haplogroup H, popularly known as "Clan Helena."
FamilyTreeDNA offers two levels of basic mtDNA testing: either just the hypervariable regions (HVR1+HVR2) or a FMS (Full Mitochondrial Sequence).
The FMS is, obviously, the more refined test.