Haplogroups
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.
The article Harris (name) is a useful example, chosen for its links to two surname projects and its discussion of haplogroups for one of them. Other surname-project examples are available through the external links below.
Read more about this topic: Surname DNA Project