Genetic Genealogy Research
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