In order to provide an overview
of the various DNA tests available for genealogical research, I have compiled
the following information in hopes that it will be helpful to those readers who
are contemplating such testing.
For the purpose of genealogical
research, several DNA tests are appropriate.
These tests are the Y-chromosome (Y-DNA), the mitochondrial (mtDNA), and
the autosomal (atDNA). The purpose of
this document is to provide a basic understanding of the types of tests and
what they reveal.
A copy of one’s DNA is present in
all of his bodily cells except the red blood cells and is passed down to each
of his succeeding generations. Each
individual has 23 pairs of chromosomes (one of each pair is from the mother and
one from the father) with the 23rd pair being the sex
chromosome.
The 23rd chromosome
from the mother is always an X since she does not have a Y chromosome. An X or a Y may be inherited by the fetus
from the father. If the X is inherited
from the father, the fetus will be a female with two X chromosomes (XX). If the Y is inherited from the father, the
fetus will be a male with one of each chromosome (XY).
The two X chromosomes of the
mother randomly swap information and genes.
The X chromosome that a fetus receives from its mother is a mixture of
the X chromosomes from her parents. The
X that a fetus may inherit from its father is that of the father’s mother and
is a mixture of his mother’s two X chromosomes, one that she received from her
father and one that she received from her mother. Therefore, the mixture in that X chromosome
that the fetus receives from its father is from its maternal grandparents.
The Y Chromosome DNA Test (Y-DNA) is a test only for males. It analyzes the male Y chromosome which is
transmitted ONLY from father to son.
Therefore, the Y-DNA test provides information about the direct male
line from son to father, to his father, to his father, etc. The results are reported in markers. Several Y-DNA tests assess different amounts
of markers. Family Tree DNA offers the
following Y-DNA tests: the Y-DNA37 which
assesses 37 markers and provides matches that are likely to be related with the
past 8 generations; the Y-DNA67 which assesses 67 markers and provides matches
that are likely to be related within the past 6 generations; and the Y-DNA111 which
assesses 111 markers and provides matches that are likely to be related within
the past 4 generations. Also, with the
Y-DNA test, a haplogroup is predicted.
Male halpogroups are labeled with the letters A through T. The
haplogroup provides the participant with information regarding the major
population group from which he descends.
Participants in the Y-DNA testing
program may join a FTDNA surname project in which those with the same surname
may share information.
The Mitochondrial DNA Test (mtDNA) may be taken by males and
females. The mitochondrial is a small circle of DNA found inside the cells and
has only 37 genes. It does not recombine
and is, therefore, passed on from the mother to the child without change. The mitochondrial (mtDNA) is passed from the
mother to each of her children, male or female.
Only females can pass the mtDNA to their children. The mtDNA test reveals information about
one’s direct maternal line from one’s mother, from her mother, from her mother,
etc. The mtDNA test identifies the world
origin of one’s lineage and the haplogroup to which he or she belongs. These haplogroups are continent-specific
and/or region-specific. The female
haplogroups are identified with the letters of the alphabet depending on the
system used by the testing company.
Family Tree DNA uses the Cambridge Reference Sequence, which is the
accepted mtDNA standard, using the following letters of the alphabet with their
corresponding regions: J, K – Southern
Europe; H, T, U, V, X – Northern Europe; J, N – Middle East; L, L1, L2, and L3
– Africa; A, B, C, D, F, G – Asia; and A, B, C, D, and sometimes X – Native
American. Those interested in learning
more about the female haplogroups will find The
Seven Daughters of Eve by Bryan Sykes, a genetics professor at Oxford
University, very informative.
The mtDNA test is available in
the mtDNA Plus, a mid-level assessment, and the mtDNA Full Sequence, the
highest level of assessment. The mtDNA Plus reports results in two
hypervariable regions, HVR1 and HVR2.
The matches included with these two regions are related to the past 28
generations. The mtDNA Full Sequence
reports results in all three regions, HVR1, HVR2, and the Coding Region. Matches are related within the past 16
generations.
The Autosomal Test (atDNA) is appropriate for both men and women
and provides male and female matches that are related within the last 5
generations. However, matches beyond 5
generations are frequently found, but the confidence level set by FTDNA for the
Family Finder test is 5 generations.
Family Finder is capable of identifying matches in any branch of one’s
family and is not limited solely to the paternal or maternal lines. In addition, it provides percentages of one’s
ancestral lineage such as Native American, Middle-Eastern, Jewish, African, and
Western and Eastern European. In Family
Tree DNA, the autosomal test is known as Family Finder.
The analyses of one’s 22
chromosomes (not the 23rd one) are reported in terms of centimorgans
(cMs), longest blocks, and single nucleotide polymorphism (SNPs) which is the
most common type of genetic variation among people. One may compare this information with other
matches using graphics and spreadsheets which may be accessed through the
FTDNA’s Family Finder site. In addition, relationship-ranges and
estimated-relationships are predicted for each of one’s matches. One must understand that the DNA he inherits
from his parents (50% from the father and 50% from the mother) does not represent 25% from each of the
4 sets of grandparents or 12.5% from each of the 8 individual grandparents but
is a random mixture. However, the fact
that long blocks often “stick
together” for several generations makes matching possible.
In Conclusion
Close relatives will share larger
fragments of DNA from a common ancestor and smaller segments from more distant
ancestors. Even these small segments may
hold valuable clues for the genealogist.
One cannot compare the results of
the various tests. Each test analyzes a
different segment of the DNA and reports the results using different
terminology. The haplogroups for men
with the Y-DNA test and those for women with the mtDNA tests are different and
cannot be compared.
Family Tree DNA stores one’s DNA
for 25 years so that one may upgrade to a higher level of testing without
submitting another sample. The number of
one’s matches is dependent on the size of the company’s data base. Also, if one’s lineage or surname is rare, he
may not have any matches at first, but over time as the data base grows,
participants with whom he matches will become available.
Family Tree DNA and 23andMe were
the first two companies to offer autosomal DNA testing. Family Finder through
Family Tree DNA is specifically recommended for genealogist and adoptees. 23andMe offers an autosomal DNA test called
Relative Finder, which is similar to the Family Finder developed by Family Tree
DNA. Recently, 23andMe came under
government scrutiny due to its offering health-related information based on the
participant’s genetics without the benefits of professional medical
attention. Therefore, 23andMe no longer
provides health-related information to its participants.
Ancestry.com started offering
genetic testing in 2011.
DNA testing can be used to
confirm one’s “paper trail,” to determine which family trees with the same or
variant surnames are related, to determine individuals who are or are not
related, and to provide clues for further research.
_____________________________________________________________
Sources:
“23andMe
Halts Genetic Health Reports,”
Family Tree DNA. “Products and Pricing,” http://www.familytreedna.com/products.aspx
Family Tree DNA. “Understanding DNA.”
Hill,
Richard. “Autosomal DNA Testing for Genealogy,”
Noles, Robert B, webmaster. “Understanding your Results:
mtDNA Haplogroups,”
Knowles/Knoles/Noles Family Association, DNA –
101, Knowles Surname DNA Project,
Powell,
Kimberly. “Autosomal DNA Testing for Genealogy,” About.com Guide.
Smolenyak,
Megan Smolenyak and Ann Turner. Trace
Your Roots with DNA. Holtzbrinck
Publishers, 2004.
