mtDNA Testing for Genealogy

The basic science:

The mtDNA test can be used for testing both females and males.
Only females can pass their mtDNA on to their children.
The mtDNA test uses information from the mitochondria, which is the material that surrounds the chromosomes.
mtDNA is passed from a mother to her children, essentially unchanged. (If there were no changes, each person would have exactly the same mtDNA as "Eve" and with each other.)
This test is only useful in testing the participant's mother's mother's .... mother's line.
All people who share the same "common ancestor" will carry essentially the same mtDNA and receive tests results that are also essentially the same.

How it works

The laboratory examines the DNA sample and uses standardized protocols to test the mtDNA.
The results are typically reported by designating only the differences to the Cambridge Reference Standard.
Using these differences, scientists have been able to group all people into major branches called "Haplogroups".
Results and matches are posted on the participants personal "myFTDNA" page at www.familytreedna.com
By comparing results, we can draw conclusions on which maternal lines share a common ancestor.
As this line changes names every generation, it is relatively difficult to track more than a few generations through genealogy.

Why mtDNA testing is useful

It follows only the maternal line--your mother's mother's mother's line.
While not as easy to trace as the yDNA surname matches, some mtDNA matches are able to identify common ancestor.
You will learn your maternal Haplogroup, which will tell you the ancient geographic and ethnic origins of your maternal line.
You will be able to join an mtDNA Haplogroup Project, to work with others who share your ancient origins.
You will be able to join a surname project using your mtDNA results. Although only yDNA results are useful in a surname project, by joining you will receive updates about the project, be included in the research, and be able to submit a family pedigree.

The rules for mtDNA testing

Males or females can take the mtDNA test.
The test traces your maternal line (your mother's mother's mother's...line).
You can join a Surname DNA Project if you have been mtDNA-tested, but your mtDNA results are not useful in a Surname DNA Project.
If you want to test for Native American or Jewish Ancestry, you must make sure the mtDNA test taker has a direct maternal line (through females only) back to the ancestor of interest.

mtDNA Haplogroups:

Haplogroups are used to represent the major branch points on the mitochondrial phylogenic tree.
There are random and subtle changes that allow us to see differences in different "genetic families".
These can be arranged into a "family tree of woman" that shows the different branches that have separated over 1000s and 10,000s of years.
Each person today can be assigned to a Haplogroup, which tells her (or him) their "deep ancestry".
Haplogroups are determined by looking at mutations.
The letter names of the mtDNA Haplogroups run from A to Z, and were named in the order of their discovery.
mtDNA Haplogroups are not the same as yDNA Haplogroups.

Mutations

mtDNA is passed from mother to child "essentially unchanged". However, on a random, but predictable basis for a large group, minor changes occur that we call "mutations".
We cannot predict when these mutations will occur in an individual family, but we do know that a mutation that occurs in one woman will be passed on to her children - and that her daughter will pass it on to their children, and so on ....
These mutations have occurred through the centuries, giving us the Haplogroups mentioned above,
These mutations occur less frequently than in yDNA, which makes them less useful in genealogy. Our genealogical paper trails usually extend a few hundred years on our maternal line, with a fortunate minority having paper trails reaching back further.
Many people carry mtDNA which had not experienced a mutation in the past 1000 years.