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firemonkey
09-18-2020, 02:16 PM
From Denmark.
43.3 - I shared segment
Chr 15 genomic position 20004966 - 33965738 SNP 6,144
Ethnicity in common= Scandinavian
14 shared matches none have a triangulation sign

C J Wyatt III
09-18-2020, 02:51 PM
I'd say.

Ibericus
09-18-2020, 02:57 PM
I have dozens, if not hundreds of matches in that position of ch15. Seems like MH has some work to do cleaning up these pile-up regions.

Here's a example:

Chromosome 15
Genomic position:
20004966 – 33301508
RSID:
rs118030220 – rs1375933
Segment size:
41.0 cM
Number of SNPs:
5,504

C J Wyatt III
09-18-2020, 03:28 PM
I have dozens, if not hundreds of matches in that position of ch15. Seems like MH has some work to do cleaning up these pile-up regions.

Here's a example:

Chromosome 15
Genomic position:
20004966 33301508
RSID:
rs118030220 rs1375933
Segment size:
41.0 cM
Number of SNPs:
5,504

I don't look at it as something which a DNA company needs to clean up, but instead an area which needs further understanding and explanation.

firemonkey
09-18-2020, 03:39 PM
Chr 9 33 to 71 M is my worst pile up area.

geebee
09-18-2020, 03:55 PM
I don't look at it as something which a DNA company needs to clean up, but instead an area which needs further understanding and explanation.

I agree. Pile ups are certainly real and can be very misleading. The problem is, efforts made to "clean up" matching in pile up regions sometimes affect genuine matches. Ancestry knows this is a possibility, which is one reason they suppress Timber when the shared amount is 90 cM or more.

There would be nothing wrong with Ancestry using Timber to flag matches, and maybe report total sharing both ways -- with Timber applied, and without Timber applied -- at least when there's a significant difference. As it is, though, you may never know when a genuine match has been affected.

(Now that Ancestry is reporting "longest segment", it can sometimes be obvious when Timber is at work. For example, if you have a match with total sharing of 20 cM but the longest shared segment is 50 cM. Someone on the Forum reported that Ancestry plans to report the pre-Timber total and some point, and if so that will be useful.)

Pylsteen
09-18-2020, 05:57 PM
The beginning of chr 15 is certainly a pile-up region for me too, it doesn't help that one half is from my jewish side. On the pile-up region of chr 9, I too have quite some matches, although I managed to trace the maternal side here to an ancestral couple during the mid-17th century (4 of the matches share those ancestors with me). The problem with pile-up regions IMO is, if these are regions that have a low genetic variability and tend to be inherited completely every generation, leading to an abundance of matches on these regions that may go back to medieval (or even earlier) periods, then how is it possible that so many of those matches do not triangulate? Or is the genetic variability on those segments so low that it is just very difficult to tell?

C J Wyatt III
09-18-2020, 06:40 PM
The beginning of chr 15 is certainly a pile-up region for me too, it doesn't help that one half is from my jewish side. On the pile-up region of chr 9, I too have quite some matches, although I managed to trace the maternal side here to an ancestral couple during the mid-17th century (4 of the matches share those ancestors with me). The problem with pile-up regions IMO is, if these are regions that have a low genetic variability and tend to be inherited completely every generation, leading to an abundance of matches on these regions that may go back to medieval (or even earlier) periods, then how is it possible that so many of those matches do not triangulate? Or is the genetic variability on those segments so low that it is just very difficult to tell?

I think most of us agree that throughout history, you can find cases of where a particular male fathered thousands of children. My theory is that pileups are a result of someone having multiple lines back to a one person.

Pylsteen
09-18-2020, 07:39 PM
I think most of us agree that throughout history, you can find cases of where a particular male fathered thousands of children. My theory is that pileups are a result of someone having multiple lines back to a one person.

Or processes such as founder effects or perhaps genetic drift similar to that in uniparentals.

geebee
09-18-2020, 07:41 PM
I think most of us agree that throughout history, you can find cases of where a particular male fathered thousands of children. My theory is that pileups are a result of someone having multiple lines back to a one person.

This may well be the source of many pileups. I think it can also have when a pair of individuals share several different ancestors along multiple paths, and those paths cross and recross multiple times. This can happen on lines in which cousin marriages were quite common. But, you also have together how many generations have passed since the most recent "connection".

For example, I have a match whose parents were 1st cousins. I'm related through both of them, so any of our shared segments might have been passed on his side through either parent (or both).

On my side, however, the shared segments can only have come from my mother, her father, and her father's mother. Prior to that, these segments could be from either of my grandfather's mother's parents, since they were 2nd cousins and my match would be related to both of them.

That still means that on my side, there would have been three "recombination events" (or "crossover transmission events") -- my grandfather's mother to my grandfather; my grandfather to my mother; and my mother to me -- since the time of the consanguineous couple.

But it may be useful, at least sometimes, to know when such a situation exists. So I'd rather not see pileups simply hidden. I'd rather be aware when they exist, or may exist, and it's useful for testing companies to note this. I don't think it's useful for them to "adjust" matching solely on this basis -- or at least without telling us when it is done, and the magnitude of the adjustment.

And as I've said on other occasions, even close relatives pass on DNA that includes pileup regions. To avoid discounting sharing between 2nd cousins, for example, Ancestry doesn't allow Timber to make an adjustment to sharing of at least 90 cM.

But 2nd cousins can share as little as 46 cM (https://dnapainter.com/tools/sharedcm), and half 2nd cousins -- those with only one great grandparent in common -- can share even less. There have still been too few DNA transmissions for pileups to be a significant factor, and yet if sharing is under 90 cM, it is "fair game" for Timber to adjust total cM. And before Ancestry started to list "longest shared segment", you'd never know when it happens.

rober_tce
09-18-2020, 10:47 PM
Chr. 15 from 20 million to 30 million, is a excess IBD region, so in this case it does.

tatals
01-13-2021, 06:18 PM
I was just about to open a thread regarding this area on chromosome 15, I'm glad I noticed this one first.

My aunt has this 'problem', too. She has A LOT of matches in this region - well, at least for an Italian. Segments go from 30 to 50cM. What is weird is that they don't necessarily match her ancestry, which is 100% Venetian - her matches are all Germanic somehow (Swedish, British or just plain German), with the slight variation of a Trentin one.

I understand this is an excess IBD area, I'm just a little weirded out. This doesn't happen with the rest of us - all os us others have mixed Italian-Portuguese-Native-American ancestry, with the exception of my Portuguese grandma, who doesn't have this pile-up either.