Aunt nephew shared dna

[lisalisa]

For example:

I share 199.7 cMs with a 2nd cousin  and 226 cMs with a 1st cousin once removed.  They are from the same line.

When I compare them in My Heritage, they only share 19.3 cMs.


Gadget

This is

Me with  A = 199.7
Me with B = 226
A with B = 19.6

You can't do this three way comparison in Ancestry. They only give the shared cMs with me.


Gadget

thank you, I find the numbers very interesting, so I would like to 'get some' from a test, and probably 'me + a match' would be enough to start with,

[Gadget]

Have you done a DNA test? If so, with which site?

[lisalisa]

Have you done a DNA test? If so, with which site?

not yet, am thinking of doing the ancestry one.

I just found/read the ancestry article about centiMorgans, though I haven't found it particularly easy to find the info on ancestry so far

https://support.ancestry.co.uk/s/article/Measuring-Relatedness

[sugarfizzle]

I've just looked at the shared DNA between two of my cousins

I share 199.7 cMs with a 2nd cousin  and 226 cMs with a 1st cousin once removed.  They are from the same line.

When I compare them in My Heritage, they only share 19.3 cMs.

Gadget

Even with different methods of measuring, this still seems like a huge difference.

Ancestry counts segments as low as 6 cM, my heritage also goes down as far as 6 cM, so they should be broadly similar.

FTDNA include very small amounts in their total cM, so would be expected to be different (higher), but their estimates of cousins take this into account, I think.

Regards Margaret

[Gadget]

Those are all the My Heritage results, Margaret, and each measurement is within the range

My 2nd cousin's relationship with my 1st cousin once removed is as a 2nd cousin one removed - range is 0-136, so 19.3 is within the  predicted range.

I think you misunderstood the relationships/measurements.

[Gadget]

This is the mini tree

 grts x 1
¦
------------------------------------
J                                        E        sibs
¦_____________               ¦
Ja          sibs      Jb            Ea      1st cousins
¦                         ¦               ¦
Jab      1st cs    Jbb           Eb      2nd cousins
¦
Jabc

Jbb = Me

The 19.3 cMs is between Eb and Jabc

[Yonnie3]

An update:
I just found out my aunt is only a half-aunt, according to my sister, that explains the dna showing a cousin for her that doesn't match me.  Also explains why she looked a little different from her sisters.  And explains why her "on paper" father divorced her mother.  I think science wins on this one. 
Being super-tired lately from working on the house, I forget how I did things.  I'm not supposed to be working like this but if I don't fix the stuff around the yard/house no-one-else will.  Anyway, I think I used GEDmatch tier1 to find the cousins that matched her but not me.  I'll look up how I did that and repeat it.

[sugarfizzle]

Those are all the My Heritage results, Margaret, and each measurement is within the range

My 2nd cousin's relationship with my 1st cousin once removed is as a 2nd cousin one removed - range is 0-136, so 19.3 is within the  predicted range.

I think you misunderstood the relationships/measurements.

I thought you meant that they both shared c 200 cM with you at ancestry and only c 20 cM with you at myheritage, i.e. only a tenth as much. I thought that would be highly unlikely, hence my comment. I understand what you mean now, that they share c 20 cM with each other. I don't know why I misunderstood, you made it very clear before that you were comparing shared match with shared match.

Regards Margaret

[sugarfizzle]

An update:
I just found out my aunt is only a half-aunt, according to my sister, that explains the dna showing a cousin for her that doesn't match me.  Also explains why she looked a little different from her sisters.

You do need a proper paper trail, as far as possible, before making any conclusions as has been said before.

You would ideally talk to your aunt, rather than your sister, about her supposed parentage.

And as for children looking a bit different from each other, that is normal, isn't it? My two daughters would not be taken for sisters by their looks alone.

I think you perhsps have to slow down a bit with your assumptions. See what comes in over the next month's and years, before making conclusions.

Regards Margaret