Tuesday, 7 May 2013

Step 1 - Where does the common ancestor sit on your tree (and your match's tree)?

The suggested relationship, or relationship range, will give you an idea of where the common ancestor sits on your family tree and your match’s family tree. For example 2nd cousins share a common great grandparent, 3rd cousins share a common great great grandparent, and so on.

This step will also give you an idea of how many possible candidates you need to consider. For example, if the suggested relationship is 3rd cousin, then you are predicted to share a common great great grandparent, and therefore there are 16 potential candidates in your tree, and another 16 potential candidates in your match’s tree.

If your Relationship
is …
… then your
Common Ancestor
is a …
No. of
possible candidates
in EACH tree
1st cousin
2nd cousin
Great grandparent
3rd cousin
2x great grandparent
4th cousin
3x great grandparent
5th cousin
4x great grandparent
6th cousin
5x great grandparent
7th cousin
6x great grandparent

I’ll be using several types of chart to illustrate the family tree. The standard chart that most people will be familiar with is a simple Vertical Pedigree Chart. The main problem with this is it takes up so much room, so I will tend to use Fan charts and Bow Tie charts instead. Men are in blue boxes, women are in pink boxes. 

Incidentally, the numbers beside each of the individuals are the ahnentafel numbers and are a very useful way of referring to the location of individual ancestors on the tree. We will be using this from time to time during what follows. A useful account of the properties of Ahnentafel numbers can be found here - http://andrsn.stanford.edu/ahnenbin.html. And you can download a gedcom with ahnentafel numbers going back 8+ generations here - https://www.dropbox.com/s/9km3iky9cg5ohmz/ahnentafel%208%20generation.ged

My Vertical Pedigree Chart, going back to my 16 great great grandparents. Males are in blue boxes, females in pink boxes. (Click on the image to see a larger version).

A Bow Tie chart – my paternal ancestors are on the left, my maternal ancestors are on the right. This chart goes back to my 3x great grandparents. Again, boys are in blue, girls in pink. Unknown male ancestors are indicated by an XY, and unknown female ancestors by an XX (mimicking the sex chromosome make-up of boys and girls).

You can download an Excel spreadsheet that allows you to generate a Bow Tie chart here - https://www.dropbox.com/s/8z3rzgsvnfm3dg1/Bow%20Tie%20Ancestral%20Chart%20template.xls 

An Ancestor Fan Chart – this one contains 7 generations and goes back to the ancestral level of 4x great grandparents. Instead of individual names, it contains ahnentafel numbers. You are number 1, your parents 2 and 3 (father, mother), your grandparents 4 to 7, and so on. The numbering always goes boy, girl, boy, girl, etc, from left to right. Men will always be an even number, women will always be odd. (Many would argue it should be the other way around ... )

This chart was generated by using PAF (Personal Ancestral File - free software from the Mormon wesbite familysearch) in association with PAF Companion (also free). You can download a gedcom with ahnentafel numbers going back 8+ generations here - https://www.dropbox.com/s/9km3iky9cg5ohmz/ahnentafel%208%20generation.ged - this can be imported into PAF to create the above chart.

A worked example
My maternal aunt J Hart (JH) matches Ms Margaret Baker (MB) thus:

The suggested relationship of 4th cousin implies a common 3x great grandparent (and therefore 32 potential candidates in each tree). However, because of the age difference (MB born c1960, JH c1920), the relationship is more likely to be 4th cousin once removed, with the common ancestor being 3x great grandparent to JH and 4x great grandparent to MB (and thus 64 potential candidates in her tree). Furthermore, at this level of relationship, estimates may be out by 1 or 2 generations, so the common ancestor may be further back, say 4-5x great grandparent for JH and 5-6x great grandparent for MB. This will further increase the number of potential candidates that we need to consider.

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