I have had quite a few known relatives test with 23andMe in the last couple of months. In the coming weeks, I will be writing a number of posts based on these results. As an introduction, I wanted to review some of the information that 23andMe and FTDNA provide in their FAQs regarding their autosomal DNA tests, Relative Finder and Family Finder. All of these percentages are estimates and will vary due to the random nature of genetic inheritance. The following statistics apply to both 23andMe's Relative Finder (RF) and FTDNA's Family Finder (FF).
Expected percentage of shared DNA between:
Parent/child/siblings = 50%
Grandparent/grandchild/aunt/uncle/nephew/niece/half-siblings = 25%
1st Cousins/great-grandparent/great aunt or uncle/grandnephew or niece = 12.5%
1st Cousins once removed = 6.25%
2nd Cousins = 3.125%
2nd Cousins once removed = 1.563%
3rd Cousins = .781%
4th Cousins = .195%
5th Cousins = .049%
6th Cousins = .012%
7th Cousins = .003%
8th Cousins = .001%
The likelihood of detecting shared DNA with a known relative significant enough to show up in RF or FF:
1st Cousins and closer: 100%
2nd Cousins: > 99%
3rd Cousins: ~ 90%
4th Cousins: ~ 45% (FTDNA says > 50%)
5th Cousins: ~ 15% (FTDNA says > 10%)
6th Cousins and more distant: < 5% (FTDNA says < 2%)
In some families, there will be situations that will complicate the above predictions, such as cousin marriages and half-siblingship, but, in general, they are the guidelines that should be used in analysis and comparisons.
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When I first got my results at 23andme, I expected my close relatives to conform to the above expected percentages. It was interesting to see how they differed. I share 54.30% with my sister, 31.39% with one paternal half sister and 23.67% with the other (this was the most surprising!), 24.64% with my paternal aunt, 14.85% with my dad's double first cousin, and 10.18% with my maternal great uncle.
ReplyDeleteI still have four kits from DNA day to give away: one is going to another one of my dad's double cousins, two are going to my maternal aunt & uncle, and one is going to a maternal great aunt. I really need to get on that and talk everyone into spitting :)
Yes you do! I sure wish I still had kits. The more I learn, the more I want to research... :-)
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