How do you identify a "natural" grandfather who has not been declared on the birth certificate? Here is one of the most recurring questions, which we will answer by giving the basic information for a start of identification by a genetic test.
Choose the DNA test
The most appropriate DNA test will be the one with which you will be more likely to find a genetic cousin depending on your ethnic origins in particular, some laboratories having more nationalities than others. But a chance factor will come into play If you quickly identify a close family member, such as a first cousin, a simple email exchange will be enough to identify the grandfather.
In most cases, you will have distant relatives. You will then need to be tested in all laboratories to increase the chances of identifying a close relative (s) but also to apply genetic genealogy techniques from the family trees of your cousins.
To reduce costs, you will need to start with the two laboratories refusing transfers: AncestryDNA and 23andMe. Then you can transfer the raw data file to the other two labs: MyHeritage and FamilyTree DNA.
Warning: ethnicity will not necessarily be an indication sufficient to identify the said grandfather. You can be French, and have as a result of Iberian origins. You have to understand the ethnic panels used to do that. The article: Are ethnicities reliable? will help you see more clearly.
Each laboratory has deployed different tools, this comparison table of the 4 genetic genealogy laboratories presents a summary
This 5-minutes video, which DNA test to choose? with links to genetic genealogy labs will help you make your choice.
The Y chromosome
This male-specific test is now less prevalent. Yet it is a valuable and powerful tool for identifying an entire paternal lineage. The DNA analysis is carried out on the Y chromosome transmitted almost identically from father to son. The Y chromosome of the great great-grandfather will be identical to that of his grandson and his paternal uncles until the oldest common ancestor of the lineage, having lived in archaeological times.
FamilyTree DNA is now the only genetic genealogy laboratory offering the consumer tools to analyze the Y chromosome. Wait for Father's Day promotions, for example, as you'll get a 20% discount on this much more expensive test than the others. To begin with, the analysis of 64 markers is sufficient.
You can also get an immediate discount if you buy the test through a project to identify genealogical lines such as the Canadian French Heritage project.
Who to have tested?
You, of course, but not that. You have 50% DNA from each of your parents. If you're looking for the grandfather on your father's side, and your father's dead, you'll need to have your mother tested. You will be able to identify the genetic cousins on the maternal side, and on the other hand, distinguish those on the paternal side!
But it will still be necessary to distinguish the genetic cousins from the side of the grandmother and the unknown grandfather. Rebelotte, if the grandmother is dead, the genetic test of a great aunt, a cousin on her side, will trace the cousins on the maternal side, and thus conversely those corresponding to the unknown grandfather!
If possible, you will also have your uncles and aunts tested on your father's side, if not your father. They inherited half of their father's DNA, so they'll have more genetic cousins!
Failing that, you'll have to have your brothers and sisters tested. You inherited about 25% of the DNA from this unknown grandfather. Your siblings too, but not the same 25%! You will thus widen the field of corresponding genetic cousins and the chance to identify the said grandfather.
As you will have understood, these are all pieces of a puzzle to be reconstructed. To identify the missing piece of the unknown grandfather, it is necessary to have to reconstruct the other branches of the family tree.
Other tools will allow you to identify family links with your genetic cousins, such as the legacy of the X chromosome for example. Not all laboratories report it. Today, you will only have this information on 23andMe and FamilyTree DNA.
You will also need to know how to use the tools of different laboratories or other sites such as DNApainter or GeneticAffairs. You can also transfer to free databases like GEDMatch, with precautions to follow because it is a public database!
And anyway, you'll need family trees in order to rebuild your family tree. Many genetic cousins don't have one, so it's up to you!
Genetic genealogy is learned, you will find the details in the book: DNA, a genealogical tool.