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16-10-2019, 16:05   #1
OU812
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Weird dna relationships

My dad has someone reporting on ancestry as a 2nd cousin with 222cM across 12 segments, but they match with me as a 5-8th cousin with just 17cM across 1 segment.

Any idea what’s going on with that or able to explain how it works out like that for me?
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16-10-2019, 21:32   #2
pinkypinky
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Does the segment you have match with your Dad's?
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16-10-2019, 21:36   #3
OU812
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I'm not sure how to check that
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16-10-2019, 22:02   #4
pinkypinky
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If you tested anywhere other than Ancestry, look at the chromosome browser. A. doesn't have one.
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16-10-2019, 22:07   #5
OU812
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He only matched on ancestry unfortunately. Any theories? (feel free to PM)
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17-10-2019, 10:22   #6
pinkypinky
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None at all.

Have you contacted the person and discussed it?
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17-10-2019, 19:15   #7
OU812
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Read but no answer unfortunately
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17-10-2019, 20:24   #8
Wyldwood
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Download your and your dad's raw DNA data from Ancestry and upload it to GEDmatch where you can view the shared chromosomes. Instructions for downloading are on Ancestry.

Ask the distant match to do the same.
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20-10-2019, 15:19   #9
ifconfig
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Statistically this can happen. It's like the long tail of a probability distribution.

The flip of the dice with the shuffliing of autosomes and recombination and the fact that you get 50% autosome contribution approx from your dad and 50% from your mother, mean that it is possible that this contribution was shuffled out.
You and a sibling will get a *different* 50% contribution from either parent.

It is unusual that it was shuffled to the degree that it is virtually undetectable in other chromosomes (but possible).

As someone said, Gedmatch could offer you an opportunity to lower the 7 centiMorgan threshold to see if there are some statistically less significant matching segments just under the thresholds which your Ancestry matching data shows for this individual.
It can happen also that people who are 6th cousins in reality might match you as 4th cousins due to statistical factors.
It is also possible that there is a statistical amplification going on with your dad's predicted relationship to this individual (unless you have a paper trail to confirm the degree of cousinship). Regardless , you would almost expect to match that person on approx 1/2 the number of matching segments as your dad does and with total/longest segments that are consistent with being 1 degree cousin distance further than your dad's predicted relationship with them.

Have you established which line this individual relates to your dad on ? His father's line or his mother's ?

--ifc

Last edited by ifconfig; 20-10-2019 at 15:23.
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20-10-2019, 23:40   #10
OU812
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Quote:
Originally Posted by ifconfig View Post
Have you established which line this individual relates to your dad on ? His father's line or his mother's ?

--ifc
It's on his father's side
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24-10-2019, 11:38   #11
KildareFan
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My brother & I took the Ancestry DNA test. One Great Grandmother was born in Co Galway, her husband in Co Westmeath; one grandmother was born Co Meath; three grandparents and two parents born Co Dublin. Many previous generations back as far as the 1700s born Wicklow and Dublin... yet my brother and I have very different DNA profiles on the map. My brother's DNA map doesn't include Co Galway at all whereas mine does, and the connections in the Dublin and Wicklow regions are weak. Not sure what to make of it at all!
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24-10-2019, 12:17   #12
pinkypinky
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Well, the locations on the map come from the places people (who you match) have indicated on their linked family trees, so I wouldn't give too much credence to it.
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24-10-2019, 15:12   #13
Ipso
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Could it be a case that there was a marriage between relatives on his side and the recombination left him with more DNA?
I’m seeing something a bit unusual at MyHeritage DNA where a first cousin is showing fairly different relatedness to matches that should be the same (although I don’t trust their accuracy, my data upload came from 23and me and my cousins from ancestry). I suspect some of these relatives may be related to me on both sides, but according to gedmatch my parents are not related.
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24-10-2019, 19:51   #14
srmf5
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Quote:
Originally Posted by Ipso View Post
Could it be a case that there was a marriage between relatives on his side and the recombination left him with more DNA?
I’m seeing something a bit unusual at MyHeritage DNA where a first cousin is showing fairly different relatedness to matches that should be the same (although I don’t trust their accuracy, my data upload came from 23and me and my cousins from ancestry). I suspect some of these relatives may be related to me on both sides, but according to gedmatch my parents are not related.
People can be related to you on both sides of your family without your parents being related. For example, the sister of my mum's great grandmother was married to the brother of my dad's 2x great grandfather. Therefore, the descendants of this couple will match both of my parents and match me higher than expected.
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