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Mitochondrial DNA testing uses mitochondrial DNA or mtDNA to identify a subject’s maternal bloodline. Mothers pass their DNA on to their children and it can be used to trace a maternal line backward over centuries. This type of DNA mutates at a slower pace than Y-DNA – DNA from a father - which means it’s easier to find ancestors further back in your bloodline than it would be with another sample. There is some evidence that fathers can also pass mitochondrial DNA on to their children, but the primary source is a subject’s mother.
There are several ways to use mtDNA. It is especially valuable for genealogical research. There are very few changes that occur over time with this type of DNA. Because of this and because it remains purer than Y-DNA, researchers have an easier time using this type of DNA to trace a person’s mother, grandmother, great-grandmother, etc. It’s so accurate that ruling out someone as a subject’s cousin could make it possible to determine one matrilineal line from another.
In simple terms: There’s a lot less “These people could be related because there is some trace of shared DNA” and more “These people are related because they share this DNA.”
One of the most beneficial uses of mtDNA is to identify someone’s biological mother or biological maternal relatives after a closed or anonymous adoption. If an adoptee wishes to search for his or her family, mtDNA matches make it easier to identify their biological mother.
Additionally, mitochondrial DNA offers information about a person’s geographic and ethnic origins. Again, the results are highly accurate because there is so little change in this type of DNA. Your mtDNA could reveal if your maternal line hailed from Europe, Africa, or was originally Native American.
Keep in mind, Y-DNA can be used in this way too, but researchers believe the results are unlikely to be as accurate. Both Y-DNA and mtDNA have haplogroups. These groups provide a path through ancestral origins and allow you to link your DNA to a particular genetic family tree.
As accurate as it can be, mtDNA is not perfect. Because mtDNA undergoes very little change, it can be difficult to identify a genealogical timeframe. You might know that your maternal line was in Europe but because the DNA is practically the same now as it was 300 years ago, it might be difficult to know exactly when your family was in that region.
Likewise, because everyone on the maternal side shares the same mtDNA, it’s difficult to identify which female within a line is the common ancestor. A mitochondrial DNA test shows two people are maternally related, but it wouldn’t show you if the people with matching DNA are mother and daughter, sisters distant cousins, aunts and nieces, and so on.
Is There a Way to Narrow Results from Broad mtDNA Testing?
The good news is that you can narrow your field of results even more than you would have with mtDNA results alone.
Using both mtDNA and autosomal DNA testing reduces the potential pool of cousin matches.
Here’s how it works:
You conduct a mitochondrial DNA test and identify members of your maternal line. You then determine which of the autosomal matches are on that line and look for ancestors within a recent genealogical timespan.
You can also collaborate with mtDNA cousins and autosomal cousins to assemble a family tree and look for common maternal ancestors.
One of the most important things to remember is that if you are conducting genealogical research, mtDNA results alone likely won’t be enough to give you the comprehensive view of your ancestry you want. But paired with traditional genealogical evidence, it can help you round out your family tree.
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You might be wondering if you can use an mtDNA test to rule someone in or out as the subject’s father.
The answer is no.
Paternal DNA testing traces someone’s paternal ancestry. This means it looks at DNA that has been passed on from the subject’s father, which is also known as Y-DNA. It’s called that because it analyzes the Y chromosomal DNA, which is only present in males. To conduct paternal DNA testing on a female, you’d need to also test the subject’s father, brother, or grandfather. This makes it possible to establish a genetic pattern that is then used to analyze the father’s side of the family.
There are similarities between mtDNA testing and paternal DNA testing. For example:
Both mitochondrial DNA testing and paternal DNA testing show evidence of a genetic relationship. Paternal DNA testing is about 99.9 percent accurate in identifying a subject’s father or excluding a man as the father 100 percent accurately. But it can identify a subject’s mother. Likewise, mtDNA testing can identify a person’s mother and even further back through the matrilineal bloodline, but it can’t tell a person anything about his or her father.
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“Study Shows Mitochondrial DNA Can Be Passed through Fathers – What Does This Mean for Genetics?” Phys.Org, phys.org/news/2018-11-mitochondrial-dna-fathers-genetics.html.
Scientific American. “How Do Researchers Trace Mitochondrial DNA over Centuries?” Scientific American, 6 Nov. 2006, www.scientificamerican.com/article/how-do-researchers-trace/.