Genetic genealogy is the use of DNA testing in combination with traditional genealogical methods to infer relationships between individuals and find ancestors.
The publication of The Seven Daughters of Eve by Sykes in 2001, which described the seven major haplogroups of European ancestors, helped push personal ancestry testing through DNA tests into wide public notice. With the growing availability and affordability of genealogical DNA testing, genetic genealogy as a field grew rapidly. By 2003, the field of DNA testing of surnames was declared officially to have “arrived” in an article by Jobling and Tyler-Smith in Nature Reviews Genetics. The number of firms offering tests, and the number of consumers ordering them, rose dramatically.
In 2007 23andMe was the first major company to begin offering autosomal DNA testing. This is the DNA excluding the Y-chromosomes and mitochondria. It is inherited from all ancestors in recent generations and so can be used to match with other testers who may be related. Later on, companies were also able to use this data to estimate how much of each ethnicity a customer has. FamilyTreeDNA entered this market in 2010, and AncestryDNA in 2012. Since then the number of DNA tests has expanded rapidly. By 2017, the combined totals of customers at the four largest companies was nearly 10 million. Autosomal testing is now the dominant type of genealogical DNA test, and for many companies the only test they offer.
Mitochondrial DNA (mtDNA) testing involves sequencing at least part of the mitochondria. The mitochondria is inherited from mother to child, and so can reveal information about the direct maternal line. When two individuals have matching or near mitochondria, is can be projected that they share a common maternal-line ancestor at some point in the recent past.
Y-Chromosome DNA (Y-DNA) testing involves short tandem repeat (STR) and, sometimes, single nucleotide polymorphism(SNP) testing of the Y-Chromosome. The Y-Chromosome is present only in males and only reveals information on the strict-paternal line. As with the mitochondria, close matches with individuals indicate a recent common ancestor. Because surnames in many cultures are transmitted down the paternal line, this testing is often used by Surname DNA Projects.
A common component of many autosomal tests is an ethnicity prediction. The company offering the test uses computers and calculations to make a prediction of what percentage of their DNA comes from each ethnic group. A typical number of ethnic groups is at least 20. Despite this aspect of the tests being heavily promoted and advertized, many genetic genealogists have warned consumers that the results may be inaccurate, and at best are only approximate.
Genealogical DNA testing methods are in use on a longer time scale to trace human migratory patterns. For example, they determined when the first humans came to North America and what path they followed. For several years, researchers and laboratories from around the world sampled indigenous populations from around the globe in an effort to map historical human migration patterns. The National Geographic Society's Genographic Project aims to map historical human migration patterns by collecting and analyzing DNA samples from over 100,000 people across five continents. The DNA Clans Genetic Ancestry Analysis measures a person's precise genetic connections to indigenous ethnic groups from around the world.