Mitochondrial DNA (mtDNA) testing

Map of human migration out of Africa, according to Mitochondrial DNA. The numbers represent thousands of years before present time. The blue line represents the area covered in ice or tundra during the last great ice age. The North Pole is at the center. Africa, harboring the start of the migration, is at the top left and South America is at the far right.
A person's maternal ancestry can be traced using his or her Mitochondrial DNA (mtDNA). The DNA in the human mitochondria is passed down by the mother unchanged. One exception, which was linked to infertility, has been shown. Additionally, some people cite paternal DNA transmission as invalidating mtDNA testing [2], but this is not considered problematic in scholarly population genetics studies or genetic genealogy.

What gets tested
mtDNA by current conventions is divided into three regions. They are the coding region and two Hyper Variable Regions HVR1 and HVR2). All test results are compared to the mtDNA of a European in Haplogroup H2a2. This sample is known as the Cambridge Reference Sequence (CRS). A list of single nucleotide polymorphisms (SNPs) is returned. Any "mutations" or "transitions" that are found are simply differences from the CRS.
The test results are compared to another person's results to determine the time frame in which the two people shared a most recent common ancestor (MRCA). The two most common mtDNA tests are a sequence of HVR1 and a sequence of both HVR1 and HVR2. Some people are now choosing to have a full sequence performed. This is still somewhat controversial as it may reveal medical information.

Understanding test results
The most basic of mtDNA tests will sequence Hyper Variable Region 1 (HVR1). HVR1 nucleotides are numbered 16001-16569. Some test reports might omit the 16 prefix from HVR1 results. ie 519C and not 16519C.] Haplogroup
Most results include a prediction of mtDNA Haplogroup.

Human mitochondrial DNA (mtDNA) haplogroups

If you belong to a Haplogroup that is distantly related to the CRS, then the prediction may be sufficient. Some companies test for specific mutations in the coding region. For large Haplogroups, such as mtDNA Haplogroup H, an extended test is offered to assign a sub-clade.

Understanding test results

Y-DNA tests generally examine 10-67 STR markers on the Y chromosome but over 100 markers are available. STR test results provide the personal hapolotype. SNP results indicate the hapologroup.

Haplotype
A Y-DNA hapolotype is the numbered results of a genealogical Y-DNA test. Each allele value has a distinctive frequency within a population. For example, at DYS455, the results will show 8, 9, 10, 11 or 12 repeats, with 11 being most common[1]. For high marker tests the allele frequencies provide a signature for a surname lineage.
The test results are then compared to another project member's results to determine the time frame in which the two people shared a most recent common ancestor (MRCA). If the two tests match on 37 markers, there is a 50% probability that the MRCA was fewer than 5 generations ago and a 90% probability that the MRCA was fewer than 17 generations ago.
It is important to check the number of markers that will be tested before choosing a test. For example, the Genographic Project looks at only 12 markers, while most laboratories and surname projects recommend testing at least 25. The more markers that are tested, the more discriminating and powerful the results will be. A 12 marker STR test is usually not discriminating enough to provide conclusive results for a common surname.
STRs results may also indicate a likely hapologroup, though this can only be confirmed by specifically testing for that Haplogroups' single nucleotide polymorphisms (SNPs).

What gets tested

Y-DNA testing involves looking at segments of DNA on the Y chromosome (found only in males). The segments which are examined are referred to as genetic markers and occur in what is considered "junk" DNA.

STR markers
A chromosome contains sequences of repeating nucleotides known as short tandem repeats (STRs). The number of repetitions varies from one person to another and a particular number of repetitions is known as an allele of the marker. An STR on the Y chromosome is designated by a DYS number (DNA Y-chromosome Segment number). The example below shows the allele of Rumpelstiltskin's DYS393 marker is 12. That means that sequence of nucleotides repeats 12 times.

SNP markers
An SNP is a change to a single nucleotide in a DNA sequence. The relative mutation rate for an SNP is extremely low. This makes them ideal for marking the history of the human genetic tree. SNPs are named with a letter code and a number. The letter indicates the lab or research team that discovered the SNP. The number indicates the order in which it was discovered. For example M173 is the 173rd SNP documented by the group who uses the letter M.

Y chromosome (Y-DNA) testing

A man's paternal ancestry can be traced using the DNA on his Y chromosome (Y-DNA) through Y-STR Testing. This is useful because the Y chromosome, like many European surnames, passes from father to son, and can be used to help study surnames. Women who wish to determine their paternal ancestry can ask their father, brother, paternal uncle, paternal grandfather, or a cousin who shares the same paternal lineage to take a test for them.