Multiple Relationships Should Magnify Our Shared DNA?

My triple cousin has done her DNA test at  AncestryDNA.  Thankfully she is a match–but she does not appear as my “closest” cousin simply because we have three documented relationships. Just because we are related in three ways does not mean that we share three more times the DNA than one would expect. That is not how DNA inheritance works.

While none of our relationships are as close as first cousins, they are all within a range that can be detected by the autosomal test at  AncestryDNA (the word “can” was used intentionally in that sentence–see “Cousin statistics” below). It is important to remember that the predicted amount of shared DNA between a certain cousinship is just that: a prediction.  It is subject to variation.

  • Autosomal DNA statistics–from the International Society of Genetic Genealogy. The chart includes averages, but does not include the variance for this statistical distribution and does no indicate whether it is believed that the amounts of shared DNA follows a normal distribution or some other type of statistical distribution. There is some potential “swing” in these averages.
  • Cousin statistics–from the International Society of Genetic Genealogy.

The predicted cousinship at AncestryDNA is that we are between 4th and 6th cousins. We share 21.4 centimorgans of DNA across two DNA segments. That prediction is based on our number of shared centimorgans.

This cousin and I are related in three ways:

  • second cousins, once removed–my great-grandfather, Frederich Ufkes (1893-1960) and her grandfather, Gerd (George) Ufkes (1889-1971) were brothers.
  • fourth cousins, once removed–my 3rd great-grandmother, Maria Bruns Fecht (1831-before 1877) and her 2nd great-grandfather, Ubbe Bruns (1835-1917) were full siblings.
  • fourth cousins–our 2nd great-grandparents, Focke Jansen Goldenstein (1857-1913) [mine] and Wilhelmina Jansen Goldenstein Garrelts (1852-1893) [hers] were full siblings.

This is an important reminder that the predicted relationships at  AncestryDNA are just that: predictions.

My triple cousin and I have quite a few shared matches–including known descendants of all three families from which my cousin and I descend. I have to be careful in looking at the shared matches from my maternal ancestry as it is somewhat endogamous. It’s common for a maternal relative of mine to be related to me in more than one way (often with common ancestors born after 1800) and for two maternal relatives of mine from different families to be related to each other as well.

 

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