How do you identify a "natural" grandfather who has not been declared on a birth certificate? This is one of the most frequently asked questions, which we will answer by giving you the essential information needed to start an identification using a genetic test.

Choosing the DNA Test

The most appropriate DNA test will be the one which gives you the best chance of finding a genetic cousin according to your ethnic origins in particular, some laboratories having categorised more nationalities than others. But an element of luck 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 as many laboratories as possible to increase the chances of identifying a close relative, or relatives, but also to apply genetic genealogy techniques based on the family trees of your cousins.

To reduce costs, you will need to start with the two laboratories that refuse transfers: AncestryDNAand 23andMe. Then, you can transfer the raw data file to the other two labs: MyHeritage and FamilyTree DNA.

Warning: ethnicity will not necessarily be enough of an indicator to identify the grandfather. You can be French and your results may show Iberian origins. You need to understand the ethnic reference panels used for this. The article: Are ethnicities reliable? will help you see things more clearly.

Each laboratory has deployed different tools, this comparison table of the four genetic genealogy laboratories presents a summary.

This 5-minute video, which DNA test to choose? with links to genetic genealogy labs will help you make your choice.

The Y chromosome

This male-only test is less prevalent nowadays. 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 to those of his paternal uncles, and so on until you reach the lineage's oldest common ancestor, who 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 in particular, as you'll get a 20% discount on this test, which is much more expensive 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 project French Heritage.

Who to have tested?

You, of course, but not just you. You get 50% of your DNA from your mother and 50% from your father. If you're looking for the grandfather on your father's side, and your father is dead, you'll need to have your mother tested. This way, 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 on the side of the grandmother and the unknown grandfather. Similarly, if the grandmother is dead, the genetic test of a great aunt or a cousin on her side will enable you to trace the cousins on the maternal side, and therefore, conversely, those corresponding to the unknown grandfather.

If you are unable to test your father, if possible you will also need to have your uncles and aunts on your father's side tested. 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 this unknown grandfather's DNA. Your siblings too, but not the same 25%. This way, you will widen the field of corresponding genetic cousins and increase your chances of identifying the grandfather.

As you will have understood, it is a matter of putting together the pieces of a puzzle. To identify the missing piece of the unknown grandfather, you need to reconstruct the other branches of the family tree.

Genetic Genealogy

Other tools will enable you to identify family links with your genetic cousins, such as the inheritance of the X chromosome for example. Not all laboratories indicate it. Today, only 23andMe and FamilyTree DNA give you this information.

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, although you'll need to take certain precautions because it's a public database!

And anyway, you'll need family trees in order to build your own family tree. Many genetic cousins don't have one, so it's up to you!

Genetic genealogy is something you can learn about, you will find more details in the book: DNA, A Genealogical Tool.