Ahnentafel numbers are a compact, accurate specification of how an ancestor is related to the reference person (often the DNA tester in genetic genealogy).. The downside is most cannot read off the Ahnentafel number of any ancestor readily. Luckily most genealogical tree tools can make them visible or allow a chart to be printed with the ancestors identified using these numbers.
See the references below for how the numbers are determined. But we offer a few illustrative notes for how to determine them for any ancestor.
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The tester or reference person is always Ahnentafel number 001.
To get the numbers of the parents of any person, take the persons Ahnentafel number and multiply by 2. That is the father's number. Add one to get the mothers.
So for the reference person (or DNA tester), you get 1 x 2 = 2 for the father and 1 x 2 + 1 = 3 for the mother. Paternal grandparents would then be 2 x 2 = 4 for the grandfather and 2 x 2 + 1 = 5 for the paternal grandmother. Similarly, the maternal grandparents are 3 x 2 = 6 for the maternal grandfather and 3 x 2 +1 = 7 for the maternal grandmother. And so on.
Some patterns should become obvious. The patriline ancestor is always a power of 2. So 2, 4, 8, 16 and so on up the line. yDNA matches will always be related to one of these ancestors. The matriline ancestor is always one less than the power of 2: (1), 3, 7, 15 and so on. Any of these people (including the tester them self) will have the same mtDNA result. If a cousin shares an ancestor with you that is on your matriline, then you will both share the same mtDNA result.
The grandparents at any given generation level are all the numbers between the powers of 2. So 2 to 3 for the parents, 4 to 7 for the grandparents, 8 to 15 for the great-grandparents. And so on. So for any ancestor at generation 'n', their ahnentafel number should fall between 2n and 2(n+1)-1. And the patriline EKA that is 'n' generations away is ahnentafel number 2n. With the corresponding matriline one being 2n+1-1.
Ahnentafel Number Example
(h600.org/gen Entry for Robert Hoar III)"
(h600.org/gen Entry for Robert Hoar III)"
.
The tester or reference person is always Ahnentafel number 001.
To get the numbers of the parents of any person, take the persons Ahnentafel number and multiply by 2. That is the father's number. Add one to get the mothers.
So for the reference person (or DNA tester), you get 1 x 2 = 2 for the father and 1 x 2 + 1 = 3 for the mother. Paternal grandparents would then be 2 x 2 = 4 for the grandfather and 2 x 2 + 1 = 5 for the paternal grandmother. Similarly, the maternal grandparents are 3 x 2 = 6 for the maternal grandfather and 3 x 2 +1 = 7 for the maternal grandmother. And so on.
Some patterns should become obvious. The patriline ancestor is always a power of 2. So 2, 4, 8, 16 and so on up the line. yDNA matches will always be related to one of these ancestors. The matriline ancestor is always one less than the power of 2: (1), 3, 7, 15 and so on. Any of these people (including the tester them self) will have the same mtDNA result. If a cousin shares an ancestor with you that is on your matriline, then you will both share the same mtDNA result.
The grandparents at any given generation level are all the numbers between the powers of 2. So 2 to 3 for the parents, 4 to 7 for the grandparents, 8 to 15 for the great-grandparents. And so on. So for any ancestor at generation 'n', their ahnentafel number should fall between 2n and 2(n+1)-1. And the patriline EKA that is 'n' generations away is ahnentafel number 2n. With the corresponding matriline one being 2n+1-1.
External References
- Ahnentafel Numbers on Wikipedia