DNA Testing, Part 4 – Mitochondrial DNA, The Female Connection

In Part 1 of this series I discussed autosomal DNA, the most common type of DNA tested for genealogy by the major testing companines (AncestryDNA, Family Tree DNA and 23andMe.) Parts 2 and 3 explored Y-DNA and the y-chromosome and its application to tracing the male lines and surname projects.  In Part 4 I conclude the DNA testing series with information about mitochondrial DNA, that DNA that follows the female line.

Mitrochondrial DNA and the Female Connection

As mentioned in parts 2 and 3, Y-DNA defines male-ness. Only males have Y-DNA and they pass this down to their sons. Mitrochrondrial DNA (mtDNA) is the female component and can trace mother-line ancestry – mother inherits mtDNA from her mother, who got that same mtDNA from her mother, and so on.  There is, however, one big difference between the inheritance of Y-DNA and mtDNA. While mtDNA is passed down from mother to daughter, it is also passed down to sons. The big difference, however, is that while sons inherit mtDNA from their mother, they do not pass it on. I carry my mother’s mtDNA but my son does not. My son carries my wife’s mtDNA.

This is an important consideration in DNA testing. I do not have to rely on my mother or sister to provide a mtDNA sample. I can be tested for mtDNA, and it will be the same as if my mother or sister tested. You can see some graphics of how mtDNA applies to mother-line ancestry here.

As with Y-DNA, there are several different levels of mtDNA testing. One can test only HVR1 and HVR2 regions. For a more complete test, Family Tree DNA (FTDNA) offers a full-sequence test that covers all the normal coding regions including the HVR1 and HVR2 regions. The full sequence test can take the results back to almost 180,000 years!

I haven’t seen any definitive statistics on this, but I suspect that mtDNA is the least tested type of DNA (but it is definitely getting more popular). The primary reason for this is that genealogy research tends to concentrate on male lines because typically male surnames remain the same down through generations. Because females have in the past typically changed their surname to match their husband, it becomes easy to lose the connections to their family. This is not to say that mtDNA can’t be very useful. My Mother’s mtDNA can be traced back to her 3G-grandmother, Mary (Polly) Gilliam who was born in Virginia in the mid-1700’s. Using services like FTDNA, matches to her DNA might yield more information about Mary Gilliam and sisters and mother. I already have one perfect match to another woman, Mary Polly Hearn in the 1770’s. I have yet to establish the connection between the two – the connection could be within a relatively few generations but could be a hundred years or more.

Currently FTDNA is the only company in the U. S. that offers mtDNA testing for genealogical uses.


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