Participants in the Holden DNA Genealogy Project take a Y-STR (Y-Chromosome Short Tandem Repeat) test to determine a set of 12, 24, or 37 numbers called alleles. That set of numbers is called a haplotype which varies from person to person, but matches those who are paternally related.
An additional DNA test called the Y-DNA SNP (Single Nucleotide Polymorphism) test is used to determine a person’s haplogroup. Most people who take the STR test do not need to order the additional SNP test because their haplogroup can be predicted based on unambiguous matches to other DNA tests. If no haplogroup is shown on the results chart, it means that the prediction is uncertain based on existing results for this DNA test. In that case if the person wants to know their haplogroup, they may consider ordering a Y-DNA SNP test. Only one SNP test per group is needed to confirm results for everyone in the group. Haplogroups in the results table marked by an asterisk have been identified by doing the additional SNP DNA test.
The SNP markers in a person’s Y-chromosome (which are used to determine haplogroups) are different from the STR markers (which determine haplotypes). Because SNP mutations are extremely rare, people in the same haplogroup share a common paternal ancestor from tens of thousands of years ago. A haplogroup is defined as all of the male descendants of the single person who first showed a SNP mutation. SNP’s are used by anthropologists to identify groups and study ancient migrations. STR mutations, which are more frequent, are used by genealogists to compare people with the same surname who have the same haplotype and thus share a common ancestor within the timeframe of hundreds of years.
One way to envision it is this – if a family
tree represents all of Homo Sapiens then haplogroups are branches of the
tree and haplotypes are leaves on this tree. All of the haplotypes
that belong to the same haplogroup would be leaves on the same branch.
You and your paternal ancestors (father, grandfather, great-grandfather,
etc.) would be part of one leaf. Others on that same leaf would be
related to you in a more recent time span, but if we go back far enough
everyone is related to everyone. Every male in the world would belong
to one of the branches of this tree. Your male ancestors whose descent
to you is through a mixture of males and females (such as your maternal
grandfather) would be other leaves, likely on other branches, of this tree.
(See the anthropological Phylogenetic tree which shows how all human Y-chromosomes
are related at www.familytreedna.com/haplotree.html)
All of the participants in group A of the Holden DNA Genealogy Project (based on matching results to the SNP test for participant 001) know that they fit on the P19 branch of this Phylogenetic tree. Participants in other groups have estimated haplogroups and thus no information about their SNP markers.
The Y Chromosome Consortium has defined
18 major haplogroups, labeled A through R as capital letters. Haplogroups
can have subgroups labeled with numbers, and subgroups can have subgroups
labeled with small letters, for example I, J2, I1b, R1b. In general,
the following rule of thumb may be used (source Family Tree DNA):
The haplogroup designation for each participant is included along with his haplotype in the results table of the Holden DNA Genealogy Project.
People who have taken DNA tests can see additional information about their haplogroup by entering their kit number and code number in the Family Tree DNA home page to view their results and then clicking on the haplogroup tab. This page shows how many exact matches there are, as well as how many are close with one, two, three, or four step mutations. This data comes from a database of SNP results collected world-wide which continues to grow as more tests are added, so participants will also want to check back later to see new results. The countries listed for each match are where the person taking the test currently lives, not necessarily where his ancestors were from, but is useful information to see migratory patterns. These matches are most likely to people with different surnames, and names are not listed. Because SNP mutations are rare, close matches here are to people who share a common ancestor from tens of thousands of years ago, long before surnames were used, and thus beyond the scope of genealogists looking for relatives.
The Holden surname is believed to have originated in England, but the fact that we have Holden DNA test results in different haplogroups shows that long before 700 to 1,000 years ago, when surnames began to be used, our Holden ancestors came from different groups which migrated across Europe and settled in England. Members of R1b, which is the most common haplogroup in European populations, are thought to be descendants of those who repopulated Europe after the last Ice Age. The Vikings are believed to have been part of haplogroup I. Test results also show that none of the Holdens tested so far is Native American on their paternal side, though some are thought to have American Indian ancestors through other lines. As scientists discover more about haplogroups, we will learn more about our distant ancestors who later adopted the Holden surname and passed their Y-DNA on down to current generations.
If you want to learn more about how DNA
testing helps to understand human prehistory, two good books are:
The Journey of Man, by Spencer Wells, and
The Seven Daughters of Eve, by Bryan Sykes
Revised January 7, 2005
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