Strange DNA anomoly, help please

[stormi]

Hi all,

I have some strange results going on at AncestryDNA, I'm wondering if someone can help me understand what's going on?

I'll try and explain clearly as possible:
Four people in my family have DNA test
- My Aunt (24% shared DNA with me)
- My grand-half-uncle (4% shared DNA with me)
- My grand-half-uncle's son
- and me

The issue is, my grand-half-uncle's son isn't matching with me at all. It says 'either hasn't taken a DNA test or isn't related to you'.

But:
1. If I log into my Aunt's DNA result and see her relationship to him, she has 5% shared DNA with the father and 4% shared DNA with the son.
2. If I log into my half-grand-uncle's DNA result he has 5% shared DNA with my Aunt and 50% shared DNA with his son.

So I can conclude through DNA, looking through my Aunt and my grand-half-uncle's DNA results that his son is definitely biologically related to me. But for some reason I don't see him on mine at all, surely it should show 1% at least?

What can I make of this?

Thanks for any new perspectives.

[Ruskie]

How many cMs of DNA do the people you mention share with you? Might make it easier than referring to percentages.

DNA is passed down randomly and not everyone you have a match with matches with each other, so it might be something as simple as that.

[Gadget]

As Ruskie says, DNA is passed down somewht randomly.  The first thing you could do is to look at the table shown here:

https://dnapainter.com/tools/sharedcmv4

..to see the possible range of shared DNA/cMs that  can be shared with relatives in each category.


Gadget

[Gadget]

If you're happier with percentages, the table given in this article shows shows the ranges to expect in percentage and cMs:

https://isogg.org/wiki/Autosomal_DNA_statistics

Gadget

[Ruskie]

Thanks Gadget.

[stormi]

Thanks,

I have 275cm with my half-great-grand-uncle, according to that website, this is correct. I have 1667cm with my aunt, also good. My aunts cM with my great-grand-uncle is 369cm, and 262cm with his son, which also looks right.

So basically: We're definitely blood related, but share no DNA? Is that possible? Is it also possible there is a bug in Ancestry?

According to that website you gave me, half-3C2R should be 27cM. His son is half-1C1R to me... So it still doesn't make sense to me.

[Gadget]

Note that the tables give an average and a range - many of the ranges are 0 - nnn.   

Have a read of the this article that I referenced:

https://isogg.org/wiki/Autosomal_DNA_statistics

The only other explanation is a possible Non-paternal event (NPE) at some point.

[Gadget]

Also, Ancestry has a cut off of 8cMs or above  so if they calculate a share of less than that it would not show.

It would be worth loading the results to another site/Sites - Gedmatch or My Heritage for e.g. as Ancestry  uses a technique called Timber

See

https://blogs.ancestry.com/techroots/filtering-dna-matches-at-ancestrydna-with-timber/


Gadget