- Category: Genetics
- Published on Monday, 26 March 2007 18:00
Below are a few questions and answers given by FamilyTreeDNA in order to better understand 'haplogroups'.
What is a haplogroup?
One way to think about haplogroups is as major branches on the family tree of Homo Sapiens. These haplogroup branches characterize t he early migrations of population groups. As a result, haplogroups are usually associated with a geographic region. If haplogroups are the branches of the tree then the haplotypes represent the leaves of the tree. All of the haplotypes that belong to a particular haplogroup are leaves on the same branch. Both mtDNA and Y-DNA tests provide haplogroup information, but remember that the haplogroups nomenclature are different for each.
A Y-DNA haplogroup is defined as all of the male descendants of the single person who first showed a particular SNP mutation. A SNP mutation identifies a group who share a common ancestor far back in time, since SNPs rarely mutate. Each member of a particular haplogroup has the same SNP mutation. For a single page graphic representation of the Y chromosome haplogroup tree, please see the haplotree.
An mtDNA haplogroup is defined as all of the female descendants of the single person who first showed a particular polymorphism, or SNP mutation. Like Y-DNA SNP mutations, an mtDNA SNP mutation identifies a group who share a common ancestor far back in time.
How is my haplogroup determined?
Your haplogroup is automatically tested and confirmed for mtDNA tests. For Y-DNA tests, your haplogroup is predicted based on a large database that Family Tree DNA has for this purpose. The Y-DNA haplogroup database consists of the test results of participants in studies conducted and tested by Dr. Hammer at the University of Arizona.
Due to our high level of confidence in our prediction algorithm, most of the time a person will not be offered to order a confirmation test of their Haplogroup. However, on some occasions where we do not feel that a Haplogroup can be determined unambiguously without a test, the SNP test will be offered. For several haplogroups we can now offer Deep Clade tests, which can provide further information. To learn more, click here.
How are the haplogroups named?
The mtDNA and Y-DNA haplogroups are both named according to capitalized letters of the alphabet. Examples of mtDNA haplogroups include H, L2 and A. The mtDNA haplogroups are named as researchers differentiate different population groups.
Each of these major haplogroups, or clades, can have subgroups, or subclades. Subgroups have a numeric name which follows the haplogroup name. For example, haplogroup E has two subgroups called E1 and E2. There is also a subgroup E* which belongs to haplogroup E but not either of the defined subgroups. Subclades can also have subgroups, which are noted with lower-case characters, such as E1a or E1b.
The Y Chromosome Consortium (YCC) developed a naming system for the Y-DNA haplogroups designed to easily accommodate expansion as new groups are discovered. The YCC has defined 20 major haplogroups, called A through T, which represent the major divisions of human diversity based on SNPs on the Y-chromosome.
All Family Tree DNA explanations and terminology, including our haplogroup database, use the standard system developed by the YCC and defined in the YCC paper. The Y Chromosome Consortium scientific paper, which describes the Haplogroup naming system, can be found at the link below:
Over time, as more SNPs are discovered, the haplogroup tree will grow and the haplogroup names, or nomenclature, will change accordingly. While the haplogroup names may change, the actual SNPs do not. When a new haplogroup tree is published, it takes time for all organizations to update their systems. As a result, you will find that some sites display haplogroup names based on the older nomenclature, and other sites display haplogroup names based on the newer nomenclature. You may view the older and newer Y-Chromosome Phylogenetic Trees at the links below:
You can find more information about changes in haplogroup nomenclature below: Y-DNA Haplogroup Nomenclature FAQ.