Some people eat, sleep and chew gum, I do genealogy and write...

Saturday, August 3, 2019

The History of the Development of Genealogical DNA: Part Twelve: What do I do with my DNA Data?

Before continuing with additional history and analysis, I decided to address some of the current issues involving genealogical DNA testing. So here it goes.

Unless you are totally surprised by the results of your DNA test, you may simply end up ignoring the results after a while. The main question is what are we all supposed to do with this additional information? The answer to this question depends entirely on your involvement with genealogical research and whether or not you have a family tree associated with the DNA test you took.

If you have no involvement in the genealogical research process and either do not have a family tree on one of the DNA websites or only have a very few names in your family tree (less than 25), then you will probably only get some entertainment value from the ethnicity estimates and little else. For the dedicated genealogist, DNA testing is another tool to assist in identifying relationships when used in conjunction with carefully documented genealogical research.

For example, the closest match out of 8,548 matches from my DNA test results is a person who has 9% shared DNA at 639.3 cM (centiMorgans) In case you don't know, here is a definition of centiMorgans from the International Society of Genetic Genealogy Wiki (ISOGG).
In genetic genealogy, a centiMorgan (cM) or map unit (m.u.) is a unit of recombinant frequency which is used to measure genetic distance. It is often used to imply distance along a chromosome, and takes into account how often recombination occurs in a region. A region with few cMs undergoes relatively less recombination. The number of base pairs to which it corresponds varies widely across the genome (different regions of a chromosome have different propensities towards crossover). One centiMorgan corresponds to about 1 million base pairs in humans on average. The centiMorgan is equal to a 1% chance that a marker at one genetic locus on a chromosome will be separated from a marker at a second locus due to crossing over in a single generation. 
The genetic genealogy testing companies 23andMe, AncestryDNA, Family Tree DNA and MyHeritage DNA use centiMorgans to denote the size of matching DNA segments in autosomal DNA tests. Segments which share a large number of centiMorgans in common are more likely to be of significance and to indicate a common ancestor within a genealogical timeframe.
I share on 3.0% DNA or 210.0 cM with the next closest relative in the test results. From a very simplified standpoint, the higher you centiMorgan count with any one person, the likely your relationship. From my DNA test with, I have one sibling who has also taken the test and our match is 2,673 cM shared across 65 segments. This level of correspondence almost certainly assures me that we are siblings.

In the case of the near relative from MyHeritage, that person's lack of a family tree on the website means that I have to contact that person directly to determine the relationship. This could be as easy as sending an email or making a telephone call or be extremely difficult because the person refuses contact.

Among genealogists, using centiMorgans as a guide is a common way to judge the degree of relationship. However, as you can see from my two examples, the numbers are less useful if there is no way to determine the exact relationship through traditional research methods. In order to bypass the difficulty of contacting a completely unknown person, some genealogists recruit target individuals to determine possible DNA test results connections. This tactic may or may not be possible depending on the degree of cooperation among family members. There are family organizations that at requesting and analyzing DNA information from many people and using that information construct family trees.

OK, so now I am back to some of the history. Stay tuned.

See these previous posts:

Part One:
Part Two:
Part Three:
Part Four:
Part Five:
Part Six:
Part Seven:
Part Eight:
Part Nine:
Part Ten:
Part Eleven:

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