Updated March 16, 2020
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The most popular ancestry tests are Y chromosome (Y-DNA) testing and mitochondrial DNA (mtDNA) testing, which test direct-line paternal and maternal ancestry, respectively.
Y chromosome (Y-DNA) testing
A man's patrilineal ancestry, or male-line ancestry, can be traced using the DNA on his Y chromosome (Y-DNA) through Y-STR testing. This is useful because the Y chromosome passes down almost unchanged from father to son, i.e., the non-recombining and sex-determining regions of the Y chromosome do not change. A man's test results are compared to another man's results to determine the time frame in which the two individuals shared a most recent common ancestor or MRCA. If their test results are a perfect, or nearly perfect match, they are related within genealogy's time frame.
A Y-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. Individual Y-DNA sequences or STRs which have proved useful in genealogical DNA work are called markers, and each has a name.
Haplogroups are large groups of haplotypes that can be used to define genetic populations and are often geographically oriented.
Mitochondrial DNA (mtDNA) testing
A person's matrilineal or mother-line ancestry can be traced using the DNA in his or her mitochondria, the mtDNA, as follows: This mtDNA is passed down by the mother unchanged, to all children. If a perfect match is found to another person's mtDNA test results, one may find a common ancestor in the other relative's (matrilineal) "information table", similar to the patrilineal or Y-DNA testing case above. However, because mtDNA mutations are very rare, a nearly perfect match is not as helpful as it is for the above patrilineal case. In the matrilineal case, it takes a perfect match to be very helpful.
Autosomal DNA testing purports either to determine the "genetic percentages" of a person's ancestry from particular continents/regions or to identify the countries and "tribes" of origin on an overall basis. Admixture tests arrive at these percentages by examining SNPs, which are locations on the DNA where one nucleotide has "mutated" or "switched" to a different nucleotide. Tests' listing geographical places of origin use alleles—individual and family variations on various chromosomes across the genome analyzed with the aid of population databases. As further detailed below, this latter type of test concentrates on standard identity markers
|Ancestor||John Gilliam Goochland County, VA|