Genetic Genealogy?

Genetic genealogy is the use of DNA to determine family relationships

Here is a very plain English description of how DNA helps predict family relationships as I am using it to reconstruct the Buchans of Borthwick. 

DNA is inherited strictly as 50% from our father and 50% from our mother. However, the 50% that either parent gave to us is only about 25% of what they inherited from their parents, ie our grandparents. That approximation is because autosomal DNA is scrambled in a random way during recombination of chromosomes.  Recombination occurs every time an egg and a sperm cell merge to form a new person. Recombination is why we are different in so many ways from our siblings. This is how Ancestry illustrate random recombination, with more detail in the link at the bottom of the page.


In generational terms, the approximate proportion of intact DNA sequences we inherit from our ancestors is listed below. Descendants of our grandparents are our first cousins and there is 100% chance of matching them. We will match on a large number of segments, and some of these segments will have come from Buchan ancestors. Descendants of our x2 great grandparents are our third cousins, and there is only a 10% chance that we will not match them on any DNA, including Buchan DNA. [Note that these figures are changing on a regular basis].

Chances of inheriting particular DNA

Ancestor                                                     Cousinship                      Chance of DNA match*

grandparents - 25%                                      First                                    100%

x1 great-grandparents - 12.5%                    Second                                100%

x2 great grandparents - 6.25%                    Third                                    90%

x3 great grandparents - 3.125%                   Fourth                                 46% 

x4 great grandparents - 1.56%                     Fifth                                    15%

x5 great grandparents - 0.78%                     Sixth                                   <2%

If we flip this concept on its head, we can think about the possibility of still carrying the DNA of George and Jean in ourselves. Not every living descendant of George and Jean will carry their exact genetic signature. But those who do will appear on our DNA match lists. A critical step is to identify our Buchan match list.

George and Jean are my x4 great grandparents.  Therefore I should expect to carry only about 1.5% of their DNA in my DNA genome, if I am lucky. I will match only people who have also inherited part of that exact same 1.5% in their genome. These people will be my fifth cousins.  Extraordinarily I have found that my 5C (Mark and Ken) do match Pat G, who is their 4C1R, though sadly not me.

So let us start with finding as many of the Buchans of Borthwick as we can!


In June 2024 the people who have shared their match lists are:

My siblings Julie, Peter and Brian

My 1C1R (younger) Marnie, 1C1R (older) Pat 

My 2C1R (older) Kathryn

My 3C Vicki

My half-4C Helen (UK)

My 4C1R (older) Ronnie, Paul and Sheila (UK), Sandy (Scotland to Australia) and James (Canada)

My 5Cs Mark and Michele (Canada), Ken (USA), Lynn (Scotland to Australia) and Janice (Scotland)


See the following resources to help understand this critically important scientific method.

Ancestry post

Diahan Southard particularly her blog posts on understanding matches

Cousin statistics

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