Mitochondrial DNA – A Blast From the Past

This week, I learned about genealogical and historical records created before England created the civil registration system in 1837.[1] I’ve learned a wealth of knowledge that I look forward to using to confirm known ancestors and discover new ones through documentary research.

The lessons made me think about confirming and discovering ancestors who lived before 1837 using DNA. Autosomal DNA can be used to research ancestors about 6-8 generations back in time. For me, ancestors that lived 6-8 generations were born in the late 1700s and early 1800s. What if I want to use DNA to research ancestors even further back in time? Am I out of luck?

No, mitochondrial DNA (mtDNA) and Y-chromosomal DNA (Y-DNA) can be used to trace ancestors who lived more than 6-8 generations ago. In other words, to maximize DNA potential in family history research, use mtDNA and Y-DNA in conjunction with autosomal DNA research.

A mitochondrion is a single organelle found in most of our cells. Mitochondria is the word we hear the most that refers to the small organelles found – most often in multiple copies – in our cells. Mitochondria produce the chemical energy in our cells that is needed to help them function. The image below shows the tiny parts enclosed in mitochondria.

Mitochondrion. Cross-section and structure mitochondrion organelle.

Royalty-free image purchased from istock.com.

Mitochondrial DNA is a circular genome found in multiple copies inside mitochondria. mtDNA also has a unique inheritance pattern that makes it useful in family history research. Mothers pass mtDNA to their sons and daughters, then only the daughters pass it on to their children. Conversely, people can trace the origin of their mtDNA back to their mother’s, mother’s, mother’s, etc., ancestors along a matrilineal line. The chart below illustrates mtDNA inheritance from the woman at the top, down to her son who doesn’t pass it on, and her daughter, who passes it to her children. Her daughter passes it on to her descendants, and so on.

mtDNA is passed from mothers to their children. The maternal ancestor at the top of the chart passes mtDNA to her descendants. Women in the inheritance pattern are shown in gray circles, men are shown in gray squares.

mtDNA does not mutate often. It passes down through generations of descendants with minimal changes for hundreds or thousands of years. The changes that do occur are single nucleotide polymorphisms (SNPs), where a nucleotide varies from the reference sequence.

People who have similar mtDNA sequences belong to the same haplogroup. A haplogroup is a classification of mtDNA found among people who share a common matrilineal ancestor. The relative lack of changes in the mtDNA genome means that it’s very likely people with the same full sequence of mtDNA are related within a genealogical timeframe.

This table shows the variation between the testing companies and the mtDNA estimated and full sequence haplogroups from 5 family members who are matrilineally related. The family connection was verified by documentary evidence as well as autosomal DNA evidence. Notice the difference in the reported haplogroups.

DNA testing company	Daughter	Mother	Maternal Cousin 1	Maternal Cousin 2	Maternal Cousin 3
FTDNA	H3g1	H3g1
23andMe	H3g	H3	H3g	H	H3
Living DNA	H3g1

The best way to learn your mtDNA haplogroup is to take a full sequence mtDNA test at Family Tree DNA (FTDNA). Family Tree DNA uses “Next generation sequencing,” which looks at each of the nucleotides in the sequence of the genomes quickly.[2] FTDNA has the most precise haplogroup reporting.

23andMe and Living DNA test mtDNA with chip-based genotyping and tests selected branch-defining SNPS and report an estimated haplogroup.[3] I think of this estimated haplogroup as “getting in the ballpark range” of a haplogroup. The information is interesting and points toward a haplogroup determination.

As an undergraduate student, I worked at BYU for Dr. Mark Rowe. We worked with mtDNA from Pima Indians, and for a short time, with DNA from Egyptian mummies. Modern Pima Indian DNA was extracted from blood, and ancient Egyptian DNA was extracted from teeth. We also gathered hair samples from BYU students and extracted DNA from the follicles.

The process we used was the latest at the time and rapidly changing with advances in technology. Using extracted DNA, we ran the DNA samples through agarose gel electrophoresis to separate DNA fragments that varied in size.[4] We stained it and looked at it with a UV light. Next, we cut the DNA out of the gel, tagged it with radioactive tags, added primers and other chemicals to the DNA, and used a PCR (polymerase chain reaction) thermocycler machine to amplify it. Next, we sequenced the DNA using the Sanger sequencing method.[5] When the DNA had finished running through the vertical “gels,” we exposed the gels on x-rays. After that, we read the sequence visually base by base, looking for SNPs, or as we called them, “polymorphisms.”

If I lost anyone with the technical jargon, just know that for my lab co-workers and me, this was a fun and exciting time to be doing mtDNA research. Now the sequencing method is entirely automated, and robots and computers process many DNA samples at once. What used to take days can now be completed rapidly.

In a future blog post, I’ll explain how to use mtDNA haplogroup information in your family history research.

[1] Paul Milner, MDiv, FUGA, Diane C. Loosle, AG, CG, and Phillip B. Dunn, AG, “Pre-1837 English Research: Digging Deeper,” Salt Lake Institute of Genealogy (SLIG), 25-29 January 2021.

[2] “MtDNA testing comparison chart,” International Society of Genetic Genealogy Wiki (https://isogg.org/wiki/MtDNA_testing_comparison_chart : accessed 31 January 2021).

[3] ISOGG Wiki, “MtDNA testing comparison chart.”

[4] “Agarose gel electrophoresis for the separation of DNA fragments, NIH National Library of Medicine, National Center for Biotechnology Information (https://pubmed.ncbi.nlm.nih.gov/22546956/ : accessed 31 January 2021).

[5] “Sanger Sequencing: Introduction Principle, and Protocol,” CD Genomics Blog, 21 February 2020, CD Genomics (https://www.cd-genomics.com/blog/sanger-sequencing-introduction-principle-and-protocol/ : accessed 31 January 2021).