Because surnames are passed down from father to son in many cultures, and Y-chromosomes (Y-DNA) are passed from father to son with a predictable rate of mutation, people with the same surname can use genealogical DNA testing to determine if they share a common ancestor within recent history.
When two males share a surname, a test of their Y-chromosome markers will determine either that they are not related, or that they are related. If they are related, the number of markers tested and the number of matches at those markers determines the range of generations until their most recent common ancestor (MRCA). If the two tests match on 37 markers, there is a 50% probability that the MRCA was less than 5 generations ago and a 90% probability that the MRCA was less than 17 generations ago.
A Y-DNA test ranges from 10 to 67 markers on the Y chromosome. Most surname projects suggest at least 25 markers. Test results tell how many repeats a given subject has at a particular marker; the variations of repeats are known as alleles. For example, at DYS455, the results will show 8, 9, 10, 11 or 12 repeats. The specific results for a given individual are referred to as a haplotype. When a surname project has enough participants, it can determine one or more modal haplotypes for the surname.
Surname projects are now being hosted by testing companies. Group rates may be obtained for surname projects and some labs even store the submitted samples for a number of years at no cost to the participants. This enables additional tests to be performed as they become available.
The Y chromosome has been studied intensely and divided into Human Y-chromosome DNA haplogroups, based upon the results of the number of alleles in certain positions called markers. These "markers" have been chosen for their demonstrated ability to predict the haplogroup of the tested individual. They are tightly guarded proprietary information. Each testing company used a different set, although many are overlapping. This has allowed Y-STR database websites such as Ybase and Ysearch to convert scores from several companies and find matches within their database for submitted results.
Surname projects with more than 100 participants
Surname projects with more than 100 participants include:
Surname project databases
- Surname DNA Projects Database
- Cyndi's List - Surname DNA Studies and Projects
- Ybase surname search
- Ysearch surname search
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