Friday, 22 January 2016

Of X-boxes and Abraham’s Ancestors

Or, ‘No’ is also an answer.

I have recently posted - Big Chunks of DNA, Talking ‘Bout Our Generations - about a close autosomal DNA match I have with CG. He has only one Jewish great-grandparent, whereas I have 8, so the match between us almost certainly goes via this great-grandfather, Abraham Lewis. FamilyTreeDNA predicts that we are 2nd-to-4th Cousins, GEDmatch says our Most Recent Common Ancestor is 4.1 generations back. This puts us in 3rd-great-grandparent territory, ie a couple of generations prior to Abraham Lewis.

I ran a number of comparison tests on GEDmatch, on CG, myself, and a few other people who are closely matched to me, and who are also matched to CG. These threw up a number of possibilities, and closed off several others, but so far I haven’t been able to draw any solid conclusions as to how or where any of us match. See the Talking post for a discussion of these tests.

A major problem is that none of us seem to have full ancestral trees going back as far as we need to for these purposes - that is, 4 or 5 generations. At 4 generations we each have 16 2g-grandparents, at 5 we have 32 3g-grandparents. Here’s my current score, for ancestors whose given names and surnames I know:

parents: 2/2
grandparents: 4/4
great-grandparents: 8/8
2g-grandparents: 12/16, plus 3 given names and 1 completely unknown
3g-grandparents: 13/32, plus 3 given names, and 16 complete unknowns

That is a seriously incomplete tree, once you get down to my 3g-grandparents, and few of the others in the sample seem to have any more in theirs.

What about the X?
One test I did not take a close look at in that post was the X-Chromosome Matrix. The reason I didn’t go with the X is that it looks fiendishly difficult to interpret, but seeing as how I didn’t get as far as I’d hoped with the other tests, I thought I’d give the X a whirl.

The problem is that, as a male, I only get an X from my mother. At first sight this appears to be good news, because it means if I match someone on this chromosome, I can immediately discount my father as the source of the match - and all his ancestors. Females however get their X from both parents - this means that my mother’s X is a combination of both her father and her mother. This pattern repeats back through each succeeding generation, and should mean that we can narrow down the source of our matching X.

From the explanations I’ve seen, such as Unlocking the genealogical secrets of the X chromosome by Blaine Bettinger, this has the result that, at the level of 2g-grandparents, only 5 of your 8 maternal 2g-grandparents could contribute to an X-match, and none of your paternals could anyway. One generation further back, and the contributors form an even smaller proportion: only 8/16 maternal 3g-grandparents.

Blaine Bettinger's Male Inheritance Chart
Here’s the chart he devised - male is blue, always to the left, female pink (of course), always right (of course). I’m the blue circle in the middle, the left side is totally blank because my father didn’t give me an X. Two generations further back, and the same applies to my mother’s paternal grandfather - she got nothing from him, so neither do I. Which means that the whole of his line can be discounted for X-matching purposes. Similarly for each male that appears in my ancestry chart - they got no X from their father, only from their mother, so their father’s line doesn’t contribute to the party.

Now all I have to do is map my ancestral Tree to this chart, and do the same for anyone I have a decent X-match with, and hey presto, sooner or later we will spot someone appearing in both Trees, who would be the source of our match.

Well, following Bettinger’s chart, here’s my X-map, showing only those ancestors who could have contributed to my  X-chromosome:

4th Generation (2g-grandparents)
(m: mother, f: father)
m-f-m-f: Lejbus Kohn (1820-1884)
m-f-m-m: Marya Igla (b 1834)
m-m-f-m: Gitla Laja Glasman (1847-1872)
m-m-m-f: Aron Moise Szechtman (b 1845)
m-m-m-m: Laja Ruchla Landenbaum (b 1848)

I know them all. I have names and dates of birth, and some places, for all of them. Anyone I match on the X, the match has to be through one of these. The Most Recent Common Ancestor I share with the match person is not necessarily one of these, but the X-path we share goes through one of them, so the MRCA has to be an ancestor of one of them.

However, the autosomal matches I am considering here are at least one generation further out, and this is where, once again, our paper trail doesn’t quite meet our DNA trail. Here are my potential X-donors from the generation before:

5th Generation (3g-grandparents)
m-f-m-f-m: ? ?
m-f-m-m-f: ? ?
m-f-m-m-m: ? ?
m-m-f-m-f: Pinkus Glasman (d 1895)
m-m-f-m-m: Chawa ? (d 1886)
m-m-m-f-m: ? ?
m-m-m-m-f: Jankel Hersz Landenbaum (b 1822)
m-m-m-m-m: Cyma Elbsztajn (b 1822)

I know fewer than half of them. Or, to put it another way, at this level, which is the first we come to that could possibly host our MRCA, more than half my lines go blank. Worse still, Jews in Poland were only obliged to adopt surnames in 1821, just around the time when this generation was being born. Prior to that, the Jewish custom was to use patronymics, referring to the father’s given name. It is highly likely that the parents of this generation were not born with surnames, and many of them did not have surnames when they married. This makes them extremely difficult to trace even when the records are available, to put it mildly.

So even if I had a full house of 5th Generation ancestors, and knew the given names of all of their parents, I would be extremely lucky to be able to identify an MRCA with any of them. In fact I have names for only 2 out of the 13 candidate X-donors in the 6th Generation, so it looks like Mission Well-Nigh Impossible.

Nevertheless, I gave it a go, just to see where it might lead me.

Our X-matches
Here’s the chart that I get for the group of people who match both CG and myself, for matches on the X-Chromosome, in cM (centiMorgans, the unit used for measuring matching segments of DNA on a given chromosome):
















The first thing we notice is that 4 of us do not match any other member of the group: CG, AD, BN and myself. Which immediately suggests that I need to rethink the relevance of the X-Chromosome to my match with CG. I don’t match him there. So is the X-test useless for this study?

Well, maybe not quite. We have already deduced (see earlier posts) that my match with CG is not on my father’s side, as Katy, a known 1st Cousin-Once-Removed on that side, does not appear amongst his matches. So he’s almost certainly on my mother’s side. The lack of a match on the X means that we can probably discard those lines that do make an X-contribution - the ones I tried to map above. His match with me is not an X-match, so it is probably along one of my other maternal lines, one that sooner or later passes through 2 consecutive males, so that that particular X-stream comes to a halt.

So we are maybe one small step closer to locating our MRCA - they’re probably hiding in one of the blank boxes on the maternal side of Blaine Bettinger’s chart.

The same logic applies to the other non-matches here. We need to focus on our blank boxes.

On the other hand, the ones that do match look quite promising. JMN matches with 3 others, as does RNB, including their match with each other. JMN also has the two strongest matches, with Big Chunks in common with PL (41.6cM), and with LS (27.5cM). Does this indicate a common line of X-descent for the four of them? And is their MRCA to be found along those lines? If so, what implications does this have for the results we looked at in the two earlier posts?

Our Autosomal matches
In Talkin ‘Bout Our Generations, we noticed that CG and I have reasonable autosomal matches on 3 chromosomes with PL, 2 with RNB, and one with JMN. These matches seem to be quite significant, as there’s only one other match with any other member the group, a small match with YS. There is no other chromosome where any of them matches both CG and myself - they match us both, but in different places. 

What’s more, of the 3 who do match both of us, there are 2 chromosomes where 2 of them join with us to make a foursome: PL and RNB join us on a stretch of Chr 5, and PL and JMN join us on Chr 18. So CG, myself, and PL seem to form a core autosomal group, with RNB and JMN also associated. Is this a hint that some, or maybe all, of us share a single MRCA? Or maybe two MRCAs across the 5 of us, a generation apart?

And as we’ve just seen, PL, RNB and JMN are just the ones who form the core of the X-matching group. We might have a promising lead here, if it weren’t for the fact that neither CG nor I seem to match any of them on the X. However, maybe we can extract some clues from this situation.

Abraham's Ancestors
To re-cap: CG has only one Jewish g-grandparent, the rest of us have wholly Jewish ancestry, as far as I know. His match with us must come through his g-grandfather Abraham Lewis. The MRCA(s) he shares with the rest of the group must be ancestors of Abraham. So how do the rest of us connect to Abraham’s ancestors? And can our X-trails help us find our pathways to our MRCA(s)?

Let’s start with CG himself. His g-grandfather Abraham is on his father’s side, so CG has not inherited any X from his Jewish ancestors, which is why he doesn’t match on the X with any of the others in this group. However, all the rest of us can only connect to him via Abraham’s ancestors.

If I’m understanding this right, the most recent common X-ancestor of a group of people is the same person as their autosomal MRCA, it’s just that X gives us a different way of identifying them. So the X-ancestor of the core X-matching group - PL, RNB, JMN - is their MRCA. I’d really like to make the jump to say that this person is also the MRCA they share with CG, but I’m not sure that’s justified. It would be particularly nice for me, since the 5 of us - PL, RNB, JMN, CG and myself - have a reasonably good overall autosomal match, and the X-match could be pointing the way to our shared MRCA even though 2 of us don’t share in it.

Locating the X-ancestor
We can also narrow down the candidates for the common X-ancestor for each person, by tracing the lines back on Blaine Bettinger’s chart above. Both FTDNA and GEDmatch suggest our MRCA(s) lie 4 to 5 generations back. As we saw before, at 5 generations, for males there are only 8 candidates for X-donor, all on the maternal side. The lines are (m: mother, f: father):

Male pathways to X-ancestors

Of the core X-group, RNB is male, PL and JMN are female. So one of the above pathways should be RNB’s personal route to the MRCA he shares with the other two.

Females get their X from both parents, so in addition to the above pattern for the 8 lines on the maternal side of the X-chart, they also have 5 candidates on the paternal side:

Additional female pathways to X-ancestors

For PL and JMN respectively, one of these 13 pathways should be their route to the MRCA. All we need is a full family tree for each of them going back 5 generations along each of these lines. We  can then put those trees alongside the 8 candidate lines from RNB’s maternal tree, and wait for a name to jump out at us.


'No' is also an answer
My own case is different again. I know that I match CG on my maternal side, but do not match him on the X. This could be where “‘No’ is also an answer” comes in. I do not match him, so our MRCA should lie not in one of the coloured ‘candidate X-donor’ boxes in my X-chart, but in one of the blank boxes. Or, to put it another way, looking at the male-pathway list above, the path to our MRCA should lead to one of my 5th-generation ancestors who does not appear in that list - ie, to one of these:

My blank X-boxes
m-f-f-f-f: Lewek Jakobowicz (1803-1876)
m-f-f-f-m: Libe Tauba Szczawinska (d between 1852 and 1868)
m-f-f-m-f: Wolek Zegelman
m-f-f-m-m: Wajla Chern
m-f-m-f-f: ? Kohn
m-m-f-f-f: Izrael Waksman (1814-1860)
m-m-f-f-m: Chaja Gitla Ejsensztat (b 1822)
m-m-m-f-f: ? Szechtman

Amazingly, I seem to know these better than my X-match candidate ancestors (see list above). I have full names for 6 of them, and surnames for the other 2. So all I need is full lines of descent for each of them, then to put those alongside CG’s tree, and look for his 2g-grandfather Abraham Lewis, and Abraham’s parents Hyman Lisky and Rose (Lewis ?), to pop up.

Done and dusted!

Minor issues
There are a couple of minor issues that could make a bit of a mockery of my reasoning, if I’m not lucky. Many of us reckon that FTDNA, and to a lesser extent GEDmatch, overestimate the closeness of the relationships of Ashkenazi Jews. I have over 100 matches on FTDNA predicted to be at 2nd-to-4th Cousin level, but have not yet succeeded in identifying a single one of them. My guess is that most of the relationships are really a generation or two further out. That would mean looking for MRCAs at a distance of 6 to 7 generations. I have the given names of just 3 of my 128 7th-generation ancestors. 


The other issues arise from the way in which our DNA is passed on from one generation to the next. We do not necessarily receive exactly a half of our DNA from each parent, and as this is repeated over the course of a few generations, we could gradually have lost all genetic trace of one or more of our ancestors. Also, our DNA is liable to mutate over the course of the generations, and so will no longer match with people who are in fact our relatives.

These factors may be making nonsense of my argument at one point or another of this discussion. There is an outside chance that they could be behind the apparent contradictions in my interpretation of some of these tests. For instance, it is possible that CG is in fact related to me on my father’s side, but that he and/or Katy have lost some of the segments of DNA that would indicate this. The same could apply to my reading of the X data - maybe I’ve just lost the bits of X that would have indicated that I share the X-match with the core group identified above.

It is also possible that multiple instances of the endogamous relationships that are inherent amongst Ashkenazi Jews, such as cousin marriage, or just intra-community marriage over many generations, could be leading us up several garden paths at the same time.

As I have said in previous posts on this topic, I know next to nothing about genetic genealogy. I could be misunderstanding anything and everything, and making false assumptions left, right and centre. These posts represent my current grasp of the issues. Comments welcome.

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