Genetic genealogy research – Boteap.com

The completion of the human genome sequencing project was the first step in allowing scientists to unravel the secrets contained in our DNA. Also, in recent years, DNA testing has become affordable and easy to do. This has led to the practice of conducting 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 from 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 type of DNA. Mitochondrial DNA (mtDNA) is not contained in the nucleus of our cell, but in the mitochondrial organelles of our cells. These scientists chose to study mitochondrial DNA (mtDNA) due to its three unique properties which they explain as:

First, mtDNA offers an expanded 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 maternally inherited and does not recombine, it is a tool for relating individuals to each other. Third, there are about 1016 mtDNA molecules in a typical human, and they are generally identical to each other (Cann 31).

They extracted and compared the mtDNA of “147 people, drawn from five geographic populations” (Cann 31). The researchers found that “All of these mitochondrial DNAs come from a woman who is postulated to have lived about 200,000 years ago, probably in Africa” ​​(Cann 31). Their findings are also consistent with the archaeological record, as Cann explains: “mtDNA studies suggest a view of how, where, and when modern humans arose that dovetails with an interpretation of the evidence for ancient human bones and tools.” (36) .

Swedish researchers Max Ingman, Henrik Kaessmann, Svante Paabo and Ulf Gyllensten critical of these findings carried out their own study in 2000. They stated that “almost all studies of human evolution based on mtDNA sequencing have been limited to the control region, which constitutes less than 7% of the mitochondrial genome “(Ingman 708). Furthermore, they argued that previous analysis methods “provided data that are not suitable for estimates of mutation rate and thus timing of evolutionary events” (Ingman 708). So they decided to study the complete mtDNA sequence of 53 people of various races.

Surprisingly, their attempt to discredit the earlier investigation failed, as they also came to roughly the same conclusions. They yielded to the probable status of a common ancestor shared by all subjects despite not being “geographically related” (Ingman 712). They estimated “The most recent common ancestor age (MRCA) for mtDNA, based on the maximum distance between two humans … is 171,500” (Ingman 712) rather than the previous estimate of 200,000 years ago. But they refused to align their findings with archaeologists, stating that “it is not possible to determine whether the ancestors of these six extant lineages originally came from a specific geographic region” (Ingman 712). Finally, they agreed on the potential of genetic genealogy, summarizing:

Our results indicate that the field of mitochondrial population genomics will provide a rich source of genetic information for evolutionary studies. However, mtDNA is only one locus and only reflects the genetic history of females. For balanced vision, a combination of genetic systems is required. With the human genome project coming to fruition, the ease with which such data can be generated will increase, providing us with an increasingly detailed understanding of our genetic history (Ingman 712).

His call for a more balanced view was answered shortly because in 2000 a team of researchers from the Department of Genetics at Stanford University, led by Peter A. Underhill, published the results of the study of the DNA of the Y chromosome. Only males have the Y chromosome, which has unique properties, as Underhill explains:

Binary polymorphisms associated with the non-recombinant region of the human Y chromosome (NRY) preserve the paternal genetic legacy of our species that has persisted to the present, allowing inference of human evolution, population affinity, and demographic history. (358).

His report was based on “the analysis of 1,062 globally representative individuals” (Underhill 358). They concluded that the subjects “represent the descendants of the most ancient patrilines of anatomically modern humans who left Africa between 35,000 and 89,000 years ago” (Underhill 358).

Until now, genetic genealogy research has focused on these two types of DNA. As mentioned above, mtDNA is transmitted along the maternal line and DNA from the Y chromosome is transmitted along the paternal line. These two types of DNA effectively encompass all of our ancestors. However, they do not provide information about our ancestors within the covered area. For example, our maternal grandfather (the mother’s father) was unable to provide mtDNA or DNA from the Y chromosome to our mother. However, it contributed a third type of DNA called autosomal DNA. This type of DNA has yet to be studied for genetic genealogy purposes due to its inherent difficulties.

The main reason autosomal DNA is being studied now is because scientists aren’t sure how to determine which autosomal DNA comes from mom and which comes from dad without testing one or both of our parents. This situation is illustrated with the mathematical equation X = Xm / 2 + Xd / 2 where our autosomal DNA (X) is half that of our mother (Xm / 2) and half that of our father (Xd / 2). By testing ourselves, we identify our autosomal DNA, but cannot determine which part comes from mom or dad. Also, it is necessary to test one of our parents to determine exactly which parent contributed what part of our autosomal DNA. This type of test is currently used for paternity and close relationship testing. But it quickly becomes impractical after a few generations due to the difficulty of obtaining DNA samples from likely deceased ancestors.

conclusion

Genetic genealogy is the science of analyzing DNA for genealogical purposes. Studies have shown that we all come from a common male and female ancestor. Because this emerging science is so new, the benefits of this research are still being identified. I currently believe that genetic genealogy offers three categories of benefits.

First is the value of entertainment. Finding out that you are related to famous people like George Washington, Julius Caesar or Genghis Khan is just fun. Imagine the bragging rights and small talk this provides at social gatherings.

The second is the 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 pedigrees to isolate inherited diseases.

Third, there is the value of the relationship. Finding out that you are related to a wealthy person like Bill Gates can mean a financial windfall. Most important of all is the ability to reunite families. Millions of displaced and 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 test the DNA of 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. “Variation of the mitochondrial genome 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 history of human populations”. Nature Genetics 26 (2000): 358-361

Walsh, Bruce. “Estimation of 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, Eva.” Natural History 3 (2001): 32-35

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