More info Scandi Ancestry via DNA

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The source for the following, very informative article is Your Genetic Genealogist in regard to questions on the validity of Scandinavian DNa in those with English genealogical ancestry.

Email: yourgeneticgenealogist@gmail.com, California, United States

Ken Chahine, General Manager for AncestryDNA, …. was aware of the controversy surrounding the {DNA Ethnicity} admixture results, but told me that he feels more confident about their predictions since talking to Sir Walter Bodmer and Peter Donnelly of the “People of the British Isles” Wellcome Trust project at the University of Oxford.  He said that they shared information with the AncestryDNA team suggesting that they too are finding a much larger Scandinavian component in the British Isles than expected. Some of their findings can be seen in the recent article here. According to Ken, these discoveries support the notion that the British Isles was a true melting pot long before the United States earned that moniker and further suggests that there was lots of migration between the British Isles and Norway, Sweden and Denmark. Ken feels that these conclusions support AncestryDNA’s findings of significant Scandinavian admixture in many who would expect a more substantial British Isles component, like myself. I still have to wonder though if the “Scandinavian” label is a bit of a misnomer. I guess the question is: If the DNA has been in the British Isles for thousands of years, is it still “Scandinavian”? It is impossible to fully address this issue without access to the underlying genetic data on which AncestryDNA’s analysis is based.

Further addressing this issue, Ken wanted to remind all of us that our ancestors’ DNA can be diluted pretty quickly. Genetic drift comes into play, so we cannot expect our Family Tree to exactly resemble our admixture results. A good explanation of this can be found in Blaine’s blog post Everyone Has Two Family Trees – A Genealogical Tree and a Genetic Tree. This concept really only starts to come into play five or more generations deep in our family trees and shouldn’t have a substantial effect until we reach deeper than the great great great grandparent level.

Source: http://www.yourgeneticgenealogist.com/2012/06/my-review-of-ancestrydnas-admixture.html

 

Furthermore, the following extract from a  post from the Genetic Genalogist sources explains how you might vary from your parents or grandparents:

DNA is randomly passed down from generation to generation. A parent does not pass on their entire genetic makeup to a child; as a result, bits and pieces of DNA are lost in each generation.

Cousins will only share DNA if they happen to have randomly inherited that DNA from their shared ancestors. With each generation that separates the cousins, the probability that they share DNA decreases, because with every generation it is more likely that they will not inherit DNA from their ever-more-remote shared ancestors.

Third cousins, for example, share only 2 of their 16 ancestors at 4 generations. In this example, it appears that those two ancestors did not contribute an identical segment to both you and your third cousin. Interestingly, it is possible that both you and your cousin have segments of DNA from these ancestors, but they wouldn’t show up as a match in Family Inheritance or Relative Finder unless they were the same segment of DNA.

Two Family Trees

In reality, everyone has two family trees. The first is a Genealogical Tree, which is every ancestor in history that had a child who had a child who had a child that ultimately led to you. Every decision made by every person in that tree contributed to who and what you are today.

However, not every person in that tree contributed a segment of your DNA sequence (because of random inheritance, as discussed above). As a result, we have a second family tree – a Genetic Tree – which is a tree that contains only those ancestors who contributed to our DNA. No one has yet been able to construct their Genetic Tree, but soon it will be a reality thanks to advances in genetic sequencing and comparison such Relative Finder. These tools are using relatedness between people living today to deduce the inheritance of DNA from people who have been dead for centuries.
The Genetic Family Tree contains a small subset of your biological ancestors: Due to the nature of the Genealogical versus the Genetic Family Tree, entire populations, ancestors, and ethnicities are regularly lost entirely from your DNA! For example, in the following example of a Genetic Family Tree, the ethnicity in blue below is NOT part of the tree, and therefore would not be detected by a DNA test.

 

 

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