Mitochondrial DNA Testing for Genealogy: DNA Part 2

Mitochondrial DNA is passed from the mother to each of her children whether they are male or female. Both genders can be tested for mitochondrial DNA. Mitochondrial DNA is more stable than y-chromosome DNA. That means there are an even lower percentage of mutations, copying errors, between generations. Therefore, up until 2010, mitochondrial DNA has been more useful for tracing deep ancestry back hundreds or even tens of thousands of years than it has been for differentiating among different family lines in genealogical time. In this sense, genealogical time means the last few centuries when most families have had surnames. For example, a mitochondrial match at the lowest testing level may only indicate that there is a 50% chance of a common female ancestress within the last 52 generations or so. That is much too far back to have meaning in most family trees. Higher levels of testing might raise that precision up to a 50% chance of a common female ancestor within the last 20 generations; but that still is not too helpful. Until mid 2009, I was actively discouraging students and clients from testing their mitochondria unless they had a specific situation in which it could be useful. For example, it might eliminate the possibility of a close match or it might indicate some deep ethnic origin; but it would not have been useful in identifying ancestors.

At the risk of being redundant, women cannot be tested for y-chromosome DNA. On the other hand men can be tested for both mitochondrial and y-chromosome DNA. Therefore, a male, if he is tested for both, can find information about both of his parents, half of his grandparents but only two of his eight great-great-grandparents, etc. This gender difference may not seem fair but there really is a difference between girls and boys.

The precision of mitochondrial testing for the consumer genealogy market changed radically in 2009. More about that in the next installment.

Solving A Mystery With Women's DNA

Many still believe that only male DNA is useful for genealogical purposes. They need to wake up and smell DNA developments of the last 3 years. I recently helped a woman unravel an old mystery in her family using her autosomal and mitochondrial DNA test results. I will call her "Allyson" to protect the guilty dead and the living innocents. Here are some of the facts:

• The adopted daughter of Allyson’s great aunt was thought to be a family member;
• This adoptee was born in the 1920s;
• The adoptee’s daughter, who I will call "Bertha", is alive and has taken a mitochondrial DNA test and a Family Finder autosomal DNA test at FTDNA.

Speculation within the family included:

• This adoptee was the result of an illicit coupling of Allyson’s grandmother and her ex-husband long after their divorce;
• This adoptee was the result of a teenage fling of Allyson’s mother.
•  Allyson also has taken both a mitochondrial DNA test and a Family Finder autosomal DNA test at FTDNA.

The Mitochondrial DNA results:

Mitochondrial DNA is more definitive in ruling out potential relationships than in proving them. Their results could have ruled out Allyson’s mother and grandmother as potential mothers for Bertha’s mother. However, Allyson and Bertha are exact matches over all 16,569 locations on their mitochondrial DNA. They are the only exact matches for each other currently in the database. This means that the two share a direct maternal line (umbilical cord) ancestress probably within genealogical time. FTDNA says that such a match has a 50% probability of a common direct umbilical cord line ancestress within 5 generations and a 95% probability of a common direct umbilical cord ancestress within 22 generations. In this case the results do not prove how close the common ancestress actually lived, but they do add some credibility to the belief that this was an adoption within the family. Based on this result some hypotheses were formulated.

Research Hypotheses: 

#1. Bertha’s mom was the biological daughter of Allyson’s maternal grandmother and grandfather; 

#2. Bertha’s mom was the biological daughter of Allyson’s maternal grandmother and some unknown male – at least unknown to us; 

#3. Bertha’s mom was the biological daughter of Allyson’s mom and some unknown male.

No hypothesis was defined to include Allyson’s mom AND dad being the biological parents as existing letters clearly document that they did not meet until a few years after the birth of Bertha’s mother. On the other hand it can be documented that Allyson’s maternal grandmother and grandfather remained in contact long after their divorce.

Dick Eastman has famously blogged that there is no such thing as a ½ cousin. He quoted the venerable Black’s Law Dictionary to support his assertion. Well Dick, we would never be able to solve some of our genealogical mysteries unless we are able to split some cousins and other relatives in this manner.

If we want support for hypothesis # 1 above, we would need to find evidence that Allyson and Bertha could be 1^st cousins. To support hypothesis # 2 above, we would need to find evidence that Allyson and Bertha could be ½ first cousins. If hypothesis # 3 above is correct Allyson would have a ½ aunt relationship with Bertha. In these three cases Allyson and Bertha would be expected to share either about 12.5% (1^st cousins), about 6.25% (½ first cousins) or 12.5% (½ aunt). These percentages can be derived from the chart on the ISOGG Wiki: 

Cousin tree (with genetic kinship)

Relation with Adoptee’s Daughter “Bertha”	Maternal Grandmother is mother of Adoptee		Allyson’s Mother is mother
	Maternal Grandfather is Father Hypothesis #1	Maternal Grandfather is not Father Hypothesis #2	Allyson’s father is not Father of Adoptee Hypothesis #3
“Allyson”	1st cousin—12.5%	Half 1st cousin—6.25%	Half Aunt—12.5%
Male Cousin	1st cousin—12.5%	Half 1st cousin—6.25%	Half 1st cousin-once removed—3.125%
Female Cousin #1	1st cousin—12.5%	Half 1st cousin—6.25%	Half 1st cousin-once removed—3.125%
Female Cousin #2	1st cousin—12.5%	Half 1st cousin—6.25%	Half 1st cousin-once removed—3.125%

 Expected % of Shared Autosomal DNA 

for each Hypothesis

Oops! Using the autosomal data at hand we would not be able to distinguish between hypotheses 1 and 3. The expected amount of shared DNA would be the same in both cases. Fortunately there are three living 1^st cousins of Allyson who might be willing to test. Two are female and one is male. In this case their sex would not matter because we have already established the maternal haplogroup of the adoptee. All we would need is their autosomal matches with Allyson and Bertha. These cousins would not add to our ability to distinguish between options #1 and #2 because their amounts of DNA shared with Bertha should mirror those of Allyson in both cases. Both Allyson and each of the 3 cousins should be shown to be 1^st cousins with Bertha in #1 and ½ first cousins in # 2. So no increase in diagnostic ability is gained by collecting DNA from the 3 additional cousins.

But wait! We do not need them to help distinguish between #1 and #2. We might need their test results to differentiate between #1 and #3. Great! While Allyson would be a ½ aunt (sharing about 12.5%) in #3, the other 3 cousins would only be ½ 1^st cousins (sharing about 3.125%) a significant difference. So it looks like it may be possible to collect enough information to solve this mystery.

The Solution:

Actually, it turned out to be quite a bit simpler than all that. As we saw much earlier in this saga, FTDNA predicted that Allyson and Bertha were 1^st to 2^nd cousins. For our purposes that is quite an extensive range. If they share matching segments that would be expected of 1^st cousins, they would also share the amount Bertha would expect to share with a ½ aunt. But that is not the amount they share. They only share about ½ that amount. In this case it would have been easier to determine this if Allyson and Bertha had tested at 23andMe rather than FTDNA since the former reports matches in terms of % of match. FTDNA reports it in terms of centiMorgans (cMs) and SNPs matched. Although there may be handy conversion tables to translate these into % of match, Dr D had difficulty finding one. But he did find this one posted by Lindsay in her blog Confessions of a Cryokid:

According to Matt Dexter, on the FTDNA Forum, here is a breakdown of sum shared DNA ranges for various relationships:

• Parent/child: 3539-3748 centimorgans (cMs)
• 1st cousins: 548-1034 cMs
• 1st cousins once removed: 248-638 cMs
• 2nd cousins: 101-378 cMs

Although this table turned out to be very useful, it was compiled over 2 years ago. In autosomal DNA testing time that was almost light years ago. We now have tens of of thousands of more results that should have expanded our databases. Dr D would expect a currently compiled breakdown to show more overlap between the categories. 

Once the table in Lindsay's blog post was found, it showed that the 428.42 cMs shared between Allyson and Bertha were well within the expected range that would be expected for a 1^st cousin-once removed relationship.

But 1^st cousin-once removed is not one of the expected outcomes in the hypothesis table above. Or is it? Isn't it the equivalent of a ½ first cousin? I think we have a winner! The hypothesis that best meets the autosomal results is #2. The most likely biological parents of Bertha's mom are Allyson's maternal grandmother and an unknown male. Allyson's maternal grandfather seems to be ruled out as the biological father of Bertha's mother. Although testing additional cousins might lead to greater certainty, that does not appear to be necessary to identify the most likely candidate to be Bertha's grandmother. 

Mitochondrial Test now on Sale

Mitochondrial DNA tests may taken by both women and men to trace their direct maternal lines. Tests for less than full the full mitochondrial sequence are useful for deep ancestry (haplogroup) identification. However, a full sequence test is needed to narrow results to those with whom you may have matches with others within genealogical times---the last few hundred years during which we have surnames and written records. An exact match on a full mitochondrial test is thought to mean you have a 50% chance of having a common ancestress within the last 5 generations. Lower levels of testing -- even with an exact match -- only indicate you have a 50% of a common ancestress within the last 700 to 1,400 years. Most of us do not have any idea who our ancestress are that far back. :-) Therefore, a full sequence test is the only mitochondrial test that may advance your genealogical research. Lower level tests might DISprove a match but they would not prove a common ancestress had lived within recent centuries.

Subscribe to: Posts (Atom)

	mtDNA DAY SALE $129 UPGRADE ANY mtDNA TO FULL SEQUENCE
	FAMILYTREEDNA HISTORY UNEARTHED DAILY
••••••••	SPECIAL DNA DAY REDUCED PRICING	••••••••
	In 2006, Family Tree DNA pioneered the use of mitochondrial (mtDNA) full sequences to solve maternal genealogical puzzles and to produce the deepest maternal haplogroups in the industry. At that time, only a few academic researchers were using the power of the mtDNA full sequence for anthropological studies. Now 7 years later, all serious academic researchers use mtDNA full sequences for their maternal lineage research. Several prestigious institutions send their DNA samples to Family Tree DNA for complete mtDNA sequencing. Knowing that this testing level is the best value for genealogy, we have preferred to see the mtDNA full sequencing used for all genealogical purposes. However, limited lab capacity forced us to use pricing as a mechanism to control the number of orders we receive. That’s about to change! We are proud to announce we have moved our Full Sequencing line from Sanger DNA sequencing to what is called Next Generation Sequencing (NGS). This gives us much greater capacity to process tests, to reduce costs without sacrificing quality, and to ensure shorter turnaround times. We must run the entire sequence every time we process an mtDNA full sequence test, even for upgrades. However, in celebration of this advance- and National DNA Day – we’re offering our lowest price ever for upgrades to FMS. For a limited time, whether you’ve tested HVR1 or HVR1+2, you’ll be able to upgrade to the Full Sequence for just $129! Rather than the 8-10 weeks first generation sequencing required, we expect your results to be completed within 5-6 weeks. This does depend on the number of orders received though. If their DNA is already at our lab, those who order first may expect even shorter turnaround times. By upgrading to the mtDNA Full Sequence, you can see your matches at the highest resolution possible since this test sequences the entire mtDNA genome. If you belong to a subclade of your haplogroup, you’ll see that information, too. You also will be able to share your sample with the academic community at www.mtdnacommunity.org (Sharing is voluntary-some consider this a benefit!)
	THANK YOU FOR YOUR CONTINUED SUPPORT Bennett Greenspan President Family Tree DNA