Both in my personal research and in work for clients, I spend most of my time looking at the fairly recent past: the last few hundred years and the most-recent eight to ten generations. With Mother's Day approaching, I decided to dig into the deeper history of my maternal line by looking closely at my mitochondrial DNA. I've done a mitochondrial DNA full-sequence test at Family Tree DNA that tells me that I'm in Haplogroup H11a. What does that really mean?
Before I head down this rabbit hole, I'd like to go on the record saying that I don't think there's anything about my DNA that makes it more interesting or important than anyone else's, except perhaps to me (and those who share DNA with me) because I'm curious about my own stories. I'm using myself as a case study because it's the easiest DNA for me to access, and because I've already done some research on my own ancestry, so I've accumulated a fair amount of data. Over time, I hope to use this blog to describe some of the complexity of human history. Part of that will come in illustrating the complexity of my own background (again, as a case study and not because there's anything particularly remarkable about me). In terms of genetics, this requires other people to test their DNA and to give me permission to write about the results here. I also hope that other people who are not closely related to me and whose backgrounds may be very different than mine might be willing to let me share some of their stories here.
Mitochondria are organelles in our cells that generate energy. While most of our DNA is located in the nucleus of our cells, mitochondria have their own DNA. It is likely that mitochondria were once free-living bacteria that have long-since been incorporated into nearly all eukaryotic cells. Human mitochondrial DNA (mtDNA) is a small circle comprised of about 16,569 base pairs (the ladder rungs in the DNA molecule). Mitochondrial DNA is passed from biological mother to offspring; biological males have their mother's mtDNA, but do not pass it on to future generations. mtDNA doesn't undergo recombination (mixing), so except for rare mutations it is passed unchanged from mother to child. This allows us to use mtDNA to trace the deep history along the matrilineal line: my mtDNA is the same as my mother's, which is the same as her mother's, which is the same as her mother's, and so on.
Scientists have sequenced the mtDNA in living humans and in archaeological remains and used this information to create a mitochondrial family tree for all humans. This tree continues to be revised based on additional data; the most-recent version (Build 17) was published on 18 February 2016. You can see it here: http://phylotree.org/tree/index.htm . This tree shows how the patterns in chance mutations in mtDNA can be mapped back through all of our matrilineal lines to a woman known as Mitochondrial Eve who is estimated to have lived in Africa somewhere between 100,000 and 230,000 years ago. Mitochondrial Eve's mtDNA sequence has been published as the Reconstructed Sapience Reference Sequence (RSRS).1
By comparing an individual's mtDNA to the RSRS, you can see where the sequence is the same and where it differs. Those differences allow you to trace your way down the tree to one of its branches. For example, the fact that I have a G (guanine) instead of A (adenine) at positions 769 and 1018 on my mitochondrial DNA places me within the large group L3 early in the branching of the human mitochondrial tree.2 L3 later branched off into other groups that represent most maternal lineages outside of Africa. For me, that pathway goes through the following haplogroups: L3-->N-->R-->R0-->HV-->H-->H11-->H11a.
My matrilineal ancestors likely migrated from the Horn of Africa about 60,000-70,000 years ago via the Arabian peninsula and followed a southern coastal route into Asia.3 My haplogroup is a sub-group of H, which indicates that my foremothers were likely among the early farmers who migrated to Europe from Western Asia around 9,000 years ago as part of what is known as the Neolithic revolution.4 One recent study examining mitochondrial DNA from ancient human remains from what is now Germany includes a sample from an individual that shares my H11a haplogroup. This person appears to have been part of the Unetice culture in the Early Bronze Age (2200-1575 BC).5
We live in an amazing era. I can rub a bit of plastic on the inside of my cheek and for a couple hundred dollars I can know the full sequence of my mitochondrial DNA. This information can situate me in the context of research being done by scientists all over the world to examine modern and ancient mtDNA, and allows me to trace the broad outlines of my foremothers' journey from Africa to Asia to Europe. There are still huge gaps to be filled in between Bronze Age Europe and early 19th century Tennessee, which is as far as I've gotten on the paper trail for my matrilineal line. This is also just one branch of my family tree. I'm looking forward do doing similar analysis of mtDNA from other relatives, which will reveal the deep history of the matrilineal lines of other ancestors who didn't pass me their mitochondria, but were equally essential to the sequence of events that led to me.
What do you know about your matrilineal history?
1Behar DM et al., "A 'Copernican' Reassessment of the Human Mitochondrial DNA Tree from its Root," American Journal of Human Genetics 90, no. 4 (2012):675-684, doi:10.1016/j.ajhg.2012.03.002.
2There is also a third defining mutation for L3 at position 16311 with a change from C to T; in my case that position later changed back to C, which is part of what indicates that I'm part of the group H11.
3Soares, Pedro et al., "The Archaeogenetics of Europe," Current Biology 20, no. 4 (2010):R174-R183, doi:10.1016/j.cub.2009.11.054.
4Fu, Qiaomei et al., "Complete Mitochondrial Genomes Reveal Neolithic Expansion into Europe," PLOS ONE 7, no. 3 (2012):e32473, doi:10.1371/journal.pone.0032473.
5Brotherton, Paul et al., "Neolithic mitochondrial haplogroup H genomes and the genetic origins of Europeans," Nature Communications 4 (2013):1764, doi:10.1038/ncomms2656.