Wednesday, January 17, 2018

Pile-ups on Chromosomes

One intriguing question that I was looking at last year was a set of pile-ups on chromosome X in 23 and Me looking at myself and my siblings there. I wrote away to one individual who had his results on Gedmatch and he wrote back to me and hence the resurgence of that thought not resolved at the time as I had moved on to something else. With the reply I started looking at and thinking about that pileup.

I am phasing my grandparents DNA and the X chromosome, which is actually easy to work with especially if you have two brothers and two sisters plus yourself tested. Putting together the actual scenario of what it would look like was easy. The hard part was assigning the blocks. The one X is, of course, entirely completely and intact from my paternal grandmother for myself and my sisters. We all inherit the same X as that is the only X which our Father has to pass on to us. He received this singleton X from his mother who received it from her father and mother. In spite of having quite a few matches with cousins I do not have an X chromosome match with a known cousin as my closest cousin to test is a third cousin. He didn't happen to match on the X chromosome because our match is on his father's line.

The person to whom I had written shared 25 centimorgans with us on the X chromosome and the pileup that I found varied between 16 centimorgans (I didn't record less) and 28 centimorgans. The problem is that only a couple of the individuals in the pileups share DNA with one of us on other chromosomes. Reading the literature one is left with the impression that this is a somewhat resilient piece of DNA being passed down generation after generation relatively intact for some of its length. Looking at countries mentioned by the testers Ireland does stand out as a possibility for ancestry but there are many who list only the United States.

One person in particular sharing 28 centimorgans rather intrigues me. He is sharing 0.37% of his genome with one of my brothers and predicted to be a 4th cousin. He has the United Kingdom listed as the birth place of his parents with Oxford, Northampton and  Buckingham counties mentioned under other. None of these counties fit into my lines. The UK is great given my 100% UK ancestry. The five surnames he mentioned do not correspond to any of my surnames. One of the people we share in common (his suggested third cousin shares a known 4th cousin of mine descendant of my Welch-Buller family). Because he has an X match with my brother that eliminates our father's side and his father's side. That is always interesting but not enough details to go on. Perhaps I should write to him and I am contemplating doing that. I tend to write to people mostly that are on Gedmatch but do do otherwise.

Myself I share 0.27% of my genome with this individual or about 21 centimorgans. We share some of the same group in common but not entirely. My best match within this group is at 28 centimorgans.That individual also matches my brother at 23 centimorgans with whom I am sharing this other match as well but does not match my other brother and sister.

My second brother does not match this particular pileup. There is a second pileup that he matches along with another sibling. But the phasing of the X chromosome does tell me that possibility could exist in that my one brother and I match quite well on this chromosome and my other brother and one sister are a better match and do not match us. Since I have two Xs I could have two pileups with only one set matching my brother since not all of the matches are in common.

Is it possible to determine if this individual is descendant of my Welch or Buller families? I never did work through that idea at the time. But receiving a reply to my query has sent me back looking at this possibility once again. The other alternative is my Pincombe family and I would be looking at the Gray line only (John Routledge Pincombe married Grace Gray whose father was born at Etton East Riding of Yorkshire and her mother was born at Bewcastle, Cumberland). The counties mentioned as historical by the tester were Oxford, Nottingham and Buckingham. The Gray family were from Etton Yorkshire and Bewcastle Cumberland as mentioned. The Buller family was from Birmingham and Bermondsey Surrey. The Welch family was from Staffordshire and Leicestershire ending up in Birmingham. But there is also my maternal grandmother's family Taylor from Birmingham and ?. My brother only has inherited the one X chromosome from our mother and she of course inherited the Gray X from her paternal grandmother and the other X from her mother. There is also a shared match which does have a short length on another chromosome with whom I have corresponded but she is not aware of her ancestry.

The other possibility is to look at the pileup that my other brother and sister are matching. I have not yet looked at that in any detail. These two share quite a bit of the X chromosome in common.

On checking at Gedmatch I discovered a set of siblings who shared about 25 centimorgans on the X chromosome but also small amounts on other chromosomes. These three siblings are matching my older and my younger sister as well as myself but not my two brothers. However, they do not show up as matches on Ancestry DNA probably sliced out with Timber! I probably should write to this grouping as we are a full match with each other at this point and both of my brothers are a no match. It is not, however, a name with which I am familiar.

Back to the pileup and the range is from 17 to 19 centimorgans and in an area where my other brother and sister both match each other but not myself and my other brother. Four members of the match are from 23 and Me and do not appear under the matches. I continued doing a search for kits that match of these two and did separate out the Chromosome 23 matches but none of them are significantly large except for one individual that I have already written who matches all of us (and she is a recent match (still light green on Gedmatch). She is an X match however to my sister only. On the other chromosomes where this new tester matches us the phasing that I have done thus far implies a Buller-Welch connection. If true then this match alone would solve the original question. Can I resolve the sections on Chromosome 23 into my three grandparents? Since this new match does not match my other sister and I on the X chromosome but we do match our sister with the one X then the only match that works does appear to be Buller-Welch-Taylor for her and Pincombe-Gray for my other sister and myself.  For several of the chromosomes I do have a number of cousins who have tested and I am able to confidently predict that my phasing is reasonable given the known information. I shall check the matches on the other chromosomes to see if I can clearly declare these sections on Chromosome 23. None of the chromosomes on which we match have sufficiently long enough known sections to rigorously declare this to be a Buller-Welch connection. However, I shall continue to look upon this new tester as a possibility for solving this query. In the meantime her email is of the UK and perhaps in time I will hear from her.

No comments: