|
Genetic Genealogy Research
by Relative Genetics
The completion of the human genome sequencing project was the first step
in allowing scientists to unravel the secrets contained in our DNA.
Further over the past few years DNA testing has become affordable and easy
to do. This has spawned the practice of performing DNA testing for
Genealogical purposes which is called Genetic Genealogy.
One of the first
genetic genealogy studies was conducted in the late 1980s by
scientists with the Department of Biochemistry at the University of
California, Berkeley. These scientists Rebecca L. Cann, Mark Stoneking and
Allan C. Wilson studied a newly discovered kind of DNA. Mitochondrial DNA
(mtDNA) is contained not in the nucleus of our cell, but in the
mitochondria organelles of our cells. These scientists chose to study
Mitochondrial DNA (mtDNA) because of its three unique properties which
they explain as:
First, mtDNA gives a magnified view of the diversity present in the human
gene pool, because mutations accumulate in this DNA several times faster
than in the nucleus. Second, because mtDNA is inherited maternally and
does not recombine, it is a tool for relating individuals to one another.
Third, there are about 1016 mtDNA molecules within a typical human and
they are usually identical to one another (Cann 31).
They extracted and compared mtDNA from “147 people, drawn from five
geographic populations” (Cann 31). The researchers discovered that “All
these mitochondrial DNAs stem from one woman who is postulated to have
lived about 200,000 years ago, probably in Africa” (Cann 31). Their
findings also agree with the archaeology record as Cann explains “Studies
of mtDNA suggest a view of how, where and when modern humans arose that
fits with one interpretation of evidence from ancient human bones and
tools” (36).
Swedish researchers Max Ingman, Henrik Kaessmann, Svante Paabo and Ulf
Gyllensten critical of these findings conducted their own study in 2000.
They claimed that “almost all studies of human evolution based on mtDNA
sequencing have been confined to the control region, which constitutes
less than 7% of the mitochondrial genome” (Ingman 708). Further they
argued that the prior methods of analysis where “providing data that are
ill suited to estimations of mutation rate and therefore the timing of
evolutionary events” (Ingman 708). So they decided to study the complete
mtDNA sequence from 53 people of various races.
Surprisingly their attempt to discredit the previous research failed as
they also came to roughly the same conclusions. They conceded to the
likely hood of a common ancestor shared by all the subjects despite being
“geographically unrelated” (Ingman 712). They estimated “The age of the
most recent common ancestor (MRCA) for mtDNA, on the basis of the maximum
distance between two humans…to be 171,500” (Ingman 712) instead of the
earlier estimate of 200,000 years ago. But they refused to align their
findings with archeologists by stating “Whether the ancestors of these six
extant lineages originally came from a specific geographic region is not
possible to determine” (Ingman 712). Lastly they agreed on the potential
of
genetic genealogy by summarizing:
Our results indicate that the field of mitochondrial population genomics
will provide a rich source of genetic information for evolutionary
studies. Nevertheless, mtDNA is only one locus and only reflects the
genetic history of females. For a balanced view, a combination of genetic
systems is required. With the human genome project reaching fruition, the
ease by which such data may be generated will increase, providing us with
an evermore detailed understanding of our genetic history (Ingman 712).
Their call for a more balanced view was shortly answered because in 2000 a
team of researchers from the Department of Genetics at Stanford University
lead by Peter A. Underhill published their results of studying
Y-chromosome DNA. Only males have the Y-chromosome which has unique
properties as explained by Underhill:
Binary polymorphisms associated with the non-recombining region of the
human Y chromosome (NRY) preserve the paternal genetic legacy of our
species that has persisted to the present, permitting inference of human
evolution, population affinity and demographic history (358).
Their report was based upon “the analysis of 1062 globally representative
individuals” (Underhill 358). They concluded that the subjects “represent
the descendants of the most ancestral patrilineages of anatomically modern
humans that left Africa between 35,000 and 89,000 years ago” (Underhill
358).
So far genetic
genealogy research has focused on these two kinds of DNA. As mentioned
previously mtDNA is passed along the maternal line and Y-Chromosome DNA is
passed along the paternal line. These two kinds of DNA effectively
encompass all of our ancestors. Yet they provide no information about our
ancestors inside the encompassed area. For example our maternal
grandfather (mother’s father) couldn’t contribute any mtDNA or
Y-Chromosome DNA to our mother. Yet he did contribute a third type of DNA
called autosomal DNA. This type of DNA has yet to be studied for Genetic
Genealogy purposes because of its inherent difficulties.
The main reason autosomal DNA is just now being studied is because
scientists aren’t sure how to determine which autosomal DNA came from mom
and which came from dad without testing one or both of our parents. This
situation is illustrated by the mathematical equation X = Xm/2 + Xd/2
where our autosomal DNA (X) is half of our mom’s (Xm/2) and half of our
dad’s (Xd/2). By testing ourselves we identify our autosomal DNA but can’t
determine which part came from mom or dad. Additionally testing one of our
parents is necessary to determine exactly which parent contributed which
part of our autosomal DNA. This type of testing is currently used for
Paternity and near relationship testing. But quickly becomes impractical
after a few generations because of the difficulty of obtaining DNA samples
from probably deceased ancestors.
Conclusion
Genetic Genealogy is the science of analyzing DNA for genealogical
purposes. Studies have shown that we all stem from a common female and
male ancestor. Because this emerging science is so new, benefits of this
research are still being identified. Currently I believe Genetic Genealogy
offers three categories of benefits. First is entertainment value. Finding
out you’re related to famous people like George Washington, Julius Caesar
or Genghis Khan is just plain fun. Imagine the bragging rights and
small-talk fodder this provides at social gatherings. Second is scientific
value. Current studies have corroborated other scientific findings such as
the human archaeological record. Medical sciences will benefit from
correlating DNA studies with family genealogies to isolate hereditary
diseases. Third is relatedness value. Finding out you’re related to a
wealthy individual like Bill Gates may entail a financial windfall. Most
importantly of all is the ability to reunite families. Millions of
displaced war torn families and adopted children can now turn to Genetic
Genealogy to find their relatives.
Sources
Cann, Rebecca L. et al. “Mitochondrial DNA and human evolution.” Nature
325 (1987): 31-36
Carmichael, Terrence and Alexander Kuklin. How to DNA Test our Family
Relationships? California: AceN Press, 2000
Cavalli-Sforza, L. Luca et al. The History and Geography of Human Genes.
New Jersey: Princeton University Press, 1994
Ingman, Max et al. “Mitochondrial genome variation and the origin of
modern humans.” Nature 408 (2000): 708-713
Tooker, Elisabeth. An Ethnography of the Huron Indians, 1615-1649. New
York: Syracuse University Press, 1991
Underhill, Peter A. et al. “Y chromosome sequence variation and the
history of human populations.” Nature Genetics 26 (2000): 358-361
Walsh, Bruce. “Estimating the Time to the Most Recent Common Ancestor for
the Y chromosome or Mitochondrial DNA for a Pair of Individuals.” Genetics
158 (2001): 897-912
Zimmer, Carl. “After You, Eve.” Natural History 3 (2001): 32-35
Garon Yoakum is a representative for
Relative Genetics.
For more information on
genetic genealogy, contact us Toll Free at (800)956-9362
Relative Genetics may be contacted at
links@relativegenetics.com
Copyright © 2005
All Easy Cooking Recipe Kitchen
|
