Genetic Genealogy:
DNA and Family History

Looking for birth parents? At a brick wall in your family history research?

Genetic genealogy (DNA testing for family history purposes), a relatively new phenomenon, may be able to assist you!

A little Genetics for background

Please keep the following in mind when reading through these pages on genetic genealogy (DNA as it applies to family history):

DNA Molecule
Source: Flicker via
Wikimedia Commons.
DNA molecules
  • Every human being's body is made up of cells, each of which has 46 chromosomes containing DNA, with half of the genetic material in those chromosomes from each parent, arranged in pairs. These 23 chromosomes contain a person's entire genome, or hereditary information.
  • Each pair of chromosomes has one chromosome from each parent.
  • Twenty-two of the pairs are arranged the same way in both males and females. This is known as 'autosomal DNA'.
  • Each of those 22 pairs of chromosomes "recombine", so that each person has a unique combination of his or her parents' hereditary material, resulting in the infinite number of variations we see among siblings and in the human population in general.
  • The twenty-third pair is the chromosome pair which determines a person’s gender. That is:
    • Males receive an X chromosome from the mother, and a Y chromosome from the father.
    • Females have two X chromosomes, one from each parent.
  • The Y-chromosome does not combine with anything else. It passes from father to son to son, virtually unchanged.
  • Neither does the mitochondrial DNA (mtDNA). It is passed from the mother to the next generation (to both boys and girls) virtually unchanged.

Implications for Family History

The fact that the Y chromosome and the mtDNA are passed down to the next generation intact, except for some minor mutations which occur from time to time, opens up a whole realm of possibilities with respect to genetic genealogy.

For one thing, it means that it is possible to determine which males are descended from a common male ancestor.

Similarly, by testing a person’s mtDNA, both males and females can determine descent from a common female ancestor.

At the 'macro' level, genetic genealogy also has implications which go much farther back in time, inferring migration patterns of ancient peoples, using the different haplogroups (groups of males carrying the same Y-chromosome mutations, or groups of females carrying the same mtDNA mutations).

If a group of males from, say, Spain and a group of males from Polynesia were found through DNA testing to belong to the same haplogroup, then, according to genetic genealogy theory, they had a common ancestor, and it is very likely that migration from Spain to Polynesia, or vice versa, occurred at some point.

As already noted, this theory has implications for determining population migrations over time, as well as for identifying particular ethnic groups or groups in a particular geographical area who share the same mutation.

As yet, there is no agreement in the industry with respect to the definitions of ethnicity or of geographical populations, and therefore, testing of the same sample by two different laboratories, each using their own arbitrary criteria for defining these two concepts, can lead to some variation in test results regarding one's ethnic or geographic origins.

Genetic Genealogy: The Most Common Uses

The most common uses of genetic genealogy (i.e., DNA testing applied to family history) at the present time are

  • tracing the paternal ancestral line, and
  • verifying if the family history research a person has been doing is correct, since it shows whether you are genetically related to the people in your tree.

There also has been a surge of interest in genetic genealogy among African Americans, who want to discover what part of Africa their enslaved ancestors were from, and to find other relatives who were separated as a result of slave auctions. Until this technology was developed, this simply was not possible!

See the following video for an example.

Other uses for genetic genealogy include adopted persons attempting to discover their ethnic background, and to find relatives. Naturally, this is dependant on those relatives having been tested, and their data being in the same genetic database.

The History of DNA Testing

(a) Paternity Testing

Genetic genealogy is a relative newcomer on the scientific scene. While a number of important steps led up to it, such as the mapping of the chromosomes, the actual use of DNA as a tool in scientific analysis began in the 1980s, with the development of a paternity test, called “restriction fragment length polymorphism” (RFLP).

In this test, a child’s DNA is compared to that of his or her parents. Since half of the child’s chromosomes come from each parent, half of his genetic code should match his mother’s genetic code, and half should match his father’s genetic code.

If it matches half of one alleged parent's genetic code but not half of the other's, the child is not related to the second parent. This test is considered 99.99% accurate.

(b) DNA "fingerprinting" in the Courtroom

DNA “fingerprinting” began to be used in courtrooms as scientific evidence in the mid-80s. This test uses a person’s unique genetic make-up, compared to genetic evidence left at the scene of a crime or on a victim, to assist in proving or disproving a person’s presence at the scene of a crime, and ultimately his or her guilt or innocence.

This sort of DNA testing focuses on the 22 chromosomes (i.e., those other than the Y-chromosome and the mtDNA in the X chromosome), which are a "recombination" (mixing) of the chromosomal contributions from your parents, your grandparents, and their ancestors, and is unique to the individual.

(c) The PCR Technique in Paternity Testing

In the 1990s, the “polymerase chain reaction” (PCR) technique replaced RFLP as the standard in paternity testing. The RFLP method required extraction of DNA from a blood sample, and processing could take several weeks.

The PCR technique, on the other hand, can be done with samples from inside the cheek (buccal swabs), has a faster turn-around time, is less expensive, and is considered even more accurate for paternity testing than the RFLP test.

This same method is used in genetic genealogy testing, although the manner of "harvesting" the cheek cells varies from company to company (i.e., rinse with a mouthwash versus saliva in a tube versus scraping the inside of the cheeks with a little stick or tiny brush).


(d) The First Application of DNA testing to Family History: The Kohen Hypothesis

Source: Wikimedia Commons. Public Domain.

The first genetic genealogy hypothesis which led to DNA testing and an academic study occurred in the mid-1990s. At that time, nephrologist Dr. Carl Skoreki, who was of Ashkenazi Jewish descent, noted than another congregant of Sephardic Jewish background had a completely different physical appearance as compared to him. Both claimed to be of the Kohen priestly line, and therefore direct descendants of the Biblical priest Aaron.

Dr. Skoreki reasoned that, if the Jewish tradition of direct descendancy from Aaron was true, then descendants should have similar Y-chromosomal material, and presumably should retain some sort of physical resemblance to each other.

The resulting 1997 study was led by Professor Michael Hammer of the University of Arizona, a molecular geneticist who pioneered Y-chromosome research. Dr. Hammer concluded that there was one marker that was more prevalent in the Kohen Jewish population than in the general Jewish population, and that it therefore appeared to be true that a common line of descent from one man had been preserved through thousands of years.

This result, while not without its dissenters and critics (the most prevalent being that it used only 4 markers, and that some of the markers found were common in non-Jewish populations as well as those in the Kohen study), fuelled an interest in DNA testing to assist in genealogy research.

The "Kohen" test apparently has been re-run using a higher number of markers. The results indicated that the y-DNA of the Kohen men was the common among men of middle-eastern descent.

For my readers familiar with the book of Genesis in the Bible, you will recall that Abram (later known as Abraham) was of Ur of the Chaldees, a middle-eastern town whose exact location is debated. Abram was the father of both Isaac, from whom the Jewish nation are descended, and of Ishmael, from whom all the Arab nations are descended.

It therefore is not at all surprising to discover that Jewish Kohens share y-DNA with men of middle-eastern descent.

DNA testing was first offered to the public for genealogy purposes in the United States in April of 2000.

(e) Other Developments

Academic research has continued alongside the commercial offerings to the general public. Rapid advancements have been made in this field, not the least of which are the following:

  • Haplogroups (seven sub-divisions of European ancestral DNA, resulting from mutations in the Y chromosome) were reported in 2001.
  • By 2004, a method was developed to test mitochondrial DNA (mtDNA), which could detect a common female ancestor in much the same manner as the Y-chromosome testing could detect a common male ancestor.
  • Haplogroups based on mtDNA also were developed.
  • The Genographic Project, launched in 2005, recommended testing either 12 STR markers on the Y chromosome, or mutations on the HVR1 region of mtDNA.

Scientists assumed that these mutations in the Y chromosome or in the mtDNA occurred randomly, but at an identifiable rate.

By looking at the number of mutations which had occurred since the last known common ancestor, they felt that they could predict, within a reasonable margin of error, the time period during which a common ancestor of two individuals had lived, and/or the number of generations back s/he had been in their genetic line.

However, newer research has shown that some areas of mtDNA mutate much faster than others, so that the range of error for the time period of the most recent ancestor using mtDNA is broader than previously thought.

(f) Current Recommendations and Standards

Currently, the recommendation is to test at least 37 markers for a Y-chromosome test, as the more markers are tested, the more conclusive the results will be, and the more closely the time period during which the most recent common ancestor lived can be predicted.

Some laboratories offer the option of testing 67 markers, and some more than 100. The price of the test, naturally, varies according to the number of markers tested.

The following video shows this type of testing in action, in the testing of the hypothesis, by a Chinese researcher, that the Chinese were somehow different from other "races" of humans.

Clearly, genetic genealogy is still very new, and this area of science continues to develop and be refined. A number of different international genetic projects are underway, or have been concluded, using this genetic theory. The data being released point to a number of conclusions, including the following:

  • North American indigenous peoples are descended from peoples on the Asian continent;
  • Indigenous peoples in South America and the southern parts of North America were part of an earlier wave of migration than those in the far north, including the Inuit;
  • All human beings originated in Africa; and
  • There is more variation between members of a particular 'race' of people than there is between 'races'. All of the genetic markers occur in all of the 'races'.

I don't know about you, but I find genetic genealogy a fascinating area, even if it is so complex that it is difficult for scientists to explain it in laymen's terms!

Go to "DNA Testing - Tracing Family Trees with Family Finder and Relative Finder Tests"

Go to "mtDNA Testing: Genetic Genealogy and Maternal Ancestors"

Go to "Y-Chromosome DNA Testing: Gen. Gen'y and Male Ancestors"

Go to "DNA Surname Projects: Gen. Gen'y and Shared Surnames"

Go from "DNA and Family History" to "familyhistoryalive" Home Page

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