Genealogical Research with DNA
DNA – The Basics
This informative article is edited from an article written by Roberta Estes and is available on her blog DNA Explained , along with many other informative articles about DNA and Family Tree DNA testing..
Every human has 23 pairs of chromosomes, which contain most of your DNA, functional units of which are known as genes. One chromosome of each pair comes from a person’s mother and the other from their father. Due to the mixing (called recombination) of DNA that occurs during meiosis prior to sperm and egg development, each chromosome in 22 of the 23 pairs, which are known as autosomes, has DNA from both the corresponding parents (and their ancestors before them).
Two portions of our DNA are not combined with that of the other parent. The 23rd chromosome pair, in the box above, determines the sex of the individual. Two X chromosomes produce a female and an X and a Y chromosome produce a male. Women do not have a Y chromosome (otherwise they would be males) so they cannot contribute a Y chromosome to male offspring. Given this scenario, males inherit their father’s Y chromosome unmixed with the mother’s DNA, and an X chromosome from their mother, unmixed with their father’s DNA.
This inheritance pattern is what makes it possible for us to use the Y chromosome to compare against other men of the same surname to see if they share a common ancestor, because if they do, their Y chromosome DNA will match, either exactly or nearly so, because it has been passed intact directly from those paternal ancestors.
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Autosomal DNA, X chromosomal DNA and, in males, Y chromosomal DNA are all found in the nucleus of a cell. A fourth type of DNA call mitochondrial DNA, or mtDNA for short, resides within cells but outside the cell’s nucleus. Mitochondrial DNA packets are the cell’s powerhouse as they provide the entire body with energy.
For both genders, mitochondria DNA is inherited only from the mother. Men inherit their mother’s mtDNA, but do not pass it on to their offspring. Women have their mother’s mtDNA and pass it to both their female and male offspring. Given this scenario, women inherit their mother’s mtDNA unmixed with the father’s and pass it on generation to generation from female to female. This inheritance pattern is what makes it possible for us to compare our mtDNA with that of others to determine whether we share a common maternal ancestor.
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Autosomal DNA, the rest of your DNA in the other 22 chromosomes that are not the X/Y chromosome and not the mitochondrial DNA, tends to be transferred in groupings, which ultimately give us traits like Mother’s blue eyes, Grandpa’s chin or Dad’s stocky build. Sometimes these inherited traits can be less positive, like deformities, diseases or tendencies like alcoholism. How this occurs and what genes or combinations of genes are responsible for transferring particular traits is still being deciphered.
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Sometimes we inherit conflicting genes from our parents and the resolution of which trait is exhibited is called gene expression. For example, if you inherit a gene for blue eyes and brown eyes, you can’t have both, so the complex process of gene expression determines which color of eyes you will have. However, this type of genetics along with medical genetics does not concern us when we are using genetics for genealogy. Let’s focus initially on the unrecombined Y chromosomal DNA, called Y-line for short, and mtDNA as genealogical tools.
How Can Unrecombined DNA Help Us With Genealogy?
During egg and sperm cell production, called meiosis, each ancestor’s autosomal DNA gets watered down or divided by roughly half with each generation, meaning each child gets half of the DNA carried by each parent.
However, that isn’t true of the Y-line or mtDNA. In the following example of just 4 generations, we see that the Y chromosome, the blue box on the left, is passed down the paternal line intact and the son has the exact same Y-line DNA as his paternal great-grandfather.
Similarly, the round red doughnut shaped O represents the mitochondrial DNA (mtDNA) and it is passed down the maternal side, so both the daughter and the son will have the exact same mtDNA as the maternal great-grandmother (but only the female child will pass it on).
The good news is that you may well have noticed that, in most cases, the surname is passed down the same blue paternal path, so if this is a Jones family, the Y-line DNA travels right along with the surname. How it can help us with genealogy now becomes obvious, because if we can test different male descendants who also bear the Jones surname, if they share a common ancestor somewhere in recent time (the last several hundred years), their yDNA will match, or nearly so. Surname projects have been created by volunteer administrators at Family Tree DNA to facilitate coordination and comparison of individuals carrying the same or similar surnames.
Mitochondrial DNA (mtDNA) is useful as well, but not as easily for genealogical purposes since the maternal surname traditionally changes with each generation. There have been several remarkable success stories using mtDNA, but they are typically more difficult to coordinate because of the challenges presented by the last name changes. Sometimes joining regional projects is more useful for finding mtDNA matches than joining surname projects. A case in point is the Cumberland Gap projects, both Y-line and mtDNA, which have helped many people whose families lived in close proximity of the Cumberland Gap (at the intersection of Va., Tn. and Ky.) connect with their genetic cousins. In this case, mtDNA and Y-line DNA testing can confirm or refute rumors of Native American, European, African or Asian ancestry in that direct line.
What About Spontaneous Mutations?
Y-line DNA testing actually tests either 12, 25, 37, 67 or 111 locations on the Y chromosome, depending on which test you select. What is actually reported at these locations is the number of exact repeats of that segment of DNA. Occasionally, either a segment is dropped or one is added. This is a normal process and typically has no effect. However, for genealogy, these changes or mutations are wonderful, as the number of segments in a particular location will typically be the same from generation to generation. These mutations differentiate us and our families over time. Without mutations, all of our DNA would look exactly alike and there would be no genetic genealogy.
For mitochondrial DNA, you can test at the entry level, the intermediate “plus” level and at the full sequence level. If you think of the full sequence level, which tests the entire mitochondria, as a clock face, the entry level test tests from 5 till the hour to “noon” so from 11AM to 12 on the clock face. The second intermediate level tests from “noon” to 5 after, or 1PM. The full sequence level tests the entire clock face. Ultimately, if it’s matches you’re looking for, you’ll want the full sequence test to provide you with the best matches and the ones closest to you in time, plus it provides you with your full haplogroup, or clan, designation.
When a change, called a mutation, does occur at a particular location, it is then passed from father to son (or mother to daughter) and on down that line. That mutation, called a “line marker mutation” is then forever associated with that line of the family. If you test different males with the same surname, and they match except for only a couple of minor differences, you can be assured that they do in fact share a common ancestor in a genealogically relevant timeframe.
A father can potentially sire several sons, some with no mutations, and others with different mutations, as shown by the red mutation bar in the following illustration.
In the above example, John Patrick Kenney had two sons, one with no mutation and Paul Edward Kenney who had one mutation. All of the male descendents of Paul Edward Kenney have his mutation and a second mutation is added to this line at a new location in the generation above Stan Kenny.
John Patrick Kenney’s son who had no mutations sired a son Joseph Kenney, who had a mutation in yet a different location than either of the mutations in the Paul Edward Kenney line.
In the span of time between 1478 and 2004, this grouping of Kenney/Kenny families has accumulated 4 distinct lines as you can see across the bottom of the diagram, line 3 with no mutations, line 1 with 2 mutations, and two other lines with only one mutation each, but those mutations are not in the same location so they are easily differentiated in descendants testing today. These “line marker” mutations allow testers to quickly and easily see which line of the Kenny family they descend from.
What Do the Results Look Like?
At Family Tree DNA, Y DNA results are reported in the following format (where locus means the location number, the DYS# means the name of that marker location, and the number of alleles means the number of repeats of DNA found in that location). This is a partial screen shot from the Family Tree DNA results page for a participant.
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This is interesting, but the power of DNA testing isn’t in what your numbers alone look like, but in how they compare with others of similar surnames. So, you’re provided with a list of people that you match, along with access to their Gedcom file if they have uploaded one, most distant ancestor information, and most importantly, their e-mail address by clicking on the little envelope right after their name. Other DNA testing companies offer similar links to other DNA with a match to yours.
The following table is an example from the Estes surname project which has very successfully identified the various sons of the immigrant ancestor, Abraham Estes born in 1647. Based on his descendent lines’ DNA, we have even successfully reconstructed what Abraham’s DNA looked like, shown in green, through a process called triangulation, so we have a firm basis for comparison, and everyone is compared to Abraham. Mutations are highlighted in yellow (see example in the chart below). Moses through John R’s line does have line marker mutations on markers that are not shown here. Elisha’s line matches Abraham’s exactly. We have had 4 descendants test from various sons of Elisha and so far we have found no mutations.
To form a baseline within a family, we generally test two individuals from two separate lines of the common ancestor, just in case an undocumented adoption has occurred. If these two individuals match, except for minor mutations, then we know basically what the DNA of your ancestor looks like and others can then test and compare results against that established line.
If you’re a female and can’t test for y-line markers, you’re not left out. Mitochondrial results look slightly different from Y-line, but the match information is in essence the same.
What Else Can We Tell?
The results of your tests not only tell you about your genealogy, they can also tell you about your deep ancestry and identify your deep ancestral clan.
Have you ever wondered where your ancestors came from before contemporary times? We know that for the most part surnames did not exist before 1066, and in some places did not exist until much later. The likelihood of us ever knowing where our ancestors were prior to 1066, unless we are extremely lucky, is very remote using conventional genealogical research methods.
However, now with the results of our DNA, we can peer through that keyhole and unlock that door. Based on the results of our tests, and the relative rarity of the combined numbers, humans are grouped together in clans called haplogroups. We know who was a member of which clan by both the tests shown above and a different kind of test, called a SNP (pronounced snip) test.
Population geneticists use this type of information to determine how groups of people migrated, and when. We may well be able to tell if our clan is Celtic, Viking, African, Native American or even related to Genghis Khan, for example. Based on our clan type, we may be able to tell where our group resided during the last ice age, and then trace their path from there to England or America over hundreds or thousands of years. While this sounds farfetched, it certainly isn’t and many people are discovering their deep ancestry. For example, we know that the Estes clan wintered the last ice age in Anatolia, and we know this because that is where other people who have this very rare combination of marker values are found in greater numbers than anyplace else on earth.
Autosomal, the Third Kind of DNA Testing
In recent years, autosomal DNA testing has really come into its own. This type of testing does not focus on one line, like the Y-line focuses only on the direct paternal surname line and the mitochondrial focuses only on the direct maternal line. The Y-line and mtDNA are wonderful tests and provide you with huge amounts of information, but they can’t tell you anything about your other lines…not unless you can find a cousin from that other surname line and ask to have his or her DNA tested. This process is called building your DNA pedigree chart.
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You can see an example of a DNA pedigree chart below.
Autosomal testing provides you with two primary features. First, it provides you with percentages of ethnicity. This is of interest to most people. Second, you receive a list of cousin matches. These are people who match you on your autosomal results. This means that they are related to you on one line or another. It’s up to you to figure out which line from these results alone, but there are tools and techniques to utilize. You probably won’t recognize the names of most of your matches, and you may or may not recognize a common ancestor. In some cases, the genealogy isn’t far enough back or there are other challenges in identifying a common ancestor. However, some huge brick walls have fallen for people and continue to fall daily by using autosomal tools to identify common ancestral families.
See article The Autosomal Me which describes in detail how to utilize your Autosomal results.
Summary – Who Can Test For What???
Just to be sure we all understand, here’s a handy chart that summarizes who can test for what at Family Tree DNA.
Options for DNA testing
Family Tree DNA is currently the only company that offers yDNA and mtDNA testing. Both 23 and Me and Ancestry.com offer autosomal testing. Other companies may offer DNA testing, but be wary, as not all testing is legitimate
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Click on a logo below to find out more about how to have your DNA tested.
