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Posts tagged ‘cross-over’

DNA & Ethnicity


DNA can tell us a little bit about our ethnicity, but it’s more theory & speculation than hard fact. Never the less, it is fun to see what the scientists have to say about who we are. Today I am going to share the ethnicity (also referred to as admix) of the Stevens family as calculated by FamilyTreeDNA’s MyOrigins app. In another post I will show the results from other apps.

According to MyOrigins the 4 Stevens siblings are 100% European, which is certainly not surprising since my genealogy suggests our ancestors on both sides of the tree came from the British Isles. In the table below I am showing the results for each sibling as well as their average for comparison with the 2nd generation.



These are just predictions and they do not mean that we have recent ancestors that came from Northern Siberia. What this is saying is that 2% of Rose’s and 4% of Geo’s DNA signature has more in common with the current population of Finland & Northern Siberia than it does with the current population of the British Isles. It also shows that Roy and Gene do not share enough DNA markers with the current population of Finland & Northern Siberia to matter.

Each company has its own scientists and its own DNA database used for making these predictions. Therefore each company produces somewhat different ethnicity results. In addition to testing companies there are groups of scientists who have created their own prediction apps using differing methods. Many of these prediction apps are available to use for free at the website. Scientists are still working to refine their predictions. As more and more people test we will learn more about our place in the modern world and as more ancient DNA sequences become available we will learn more about our place in the ancient world.

So, why is the 2nd generation results so much different then the 1st generation.There are two basic reasons. One has to do with cross-over which I will discuss in a bit. The biggest reason for the difference between the 1st and 2nd generation is caused by the 50% contribution of the non-Stevens parent. The 2nd generation received an equal amount of DNA from each parent and will reflect the ethnicity that goes along with that non-Stevens DNA contribution. The 2nd generation is also European but there is much more diversity within that classification.

Two things stand out in the 2nd generation. First, NL and PC have significantly less British Isles then the prior generation. This is surprising because the non-Stevens parent in both cases appear to have British origins. The second surprise is the 2% non-European results for SG despite the fact the non-Stevens parent appears to be British.

So who gets the booby prize today? In the 1st generation I vote for Roy with the least amount of diversity and in the 2nd generation I vote for SG with the most surprising diversity. Where is that Central Asian coming from?

Why the Difference?

So why is there a difference in the ethnicity of these four siblings? They all have the same parents so they should have the same ethnicity shouldn’t they? Well, yes, kinda sorta.

Even though each sibling gets 50% of their DNA from the mother and 50% from the father, chromosome pairs get mixed up when egg or sperm are produced by a parent. Because of this mixing no two siblings will get exactly the same 50%. This is why siblings don’t all look the same. This mixing is random and occurs with each generation back through time. Therefore, each sibling has a unique combination of DNA from the parent and there is no guarantee any two siblings will share a specific sequence. So Rose & Geo received pieces of DNA from an ancestor with Northern Siberian like  DNA and the other two did not get that piece.

For those of us that are visual learner I have created this illustration to show how DNA segments from a particular ancestor get smaller and smaller with each generation. At about the 5th generations most segments become too small to accurately detect which ancestor they originated with. However, the ethnicity of small pieces may remain detectable for a much longer period.

DNA Recombination Illustration

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