DNA and genealogy

That there are many subtleties in the application of DNA data to genealogy can be appreciated from a simple observation. A child generally acquires 50% of its DNA from each parent, thus in effect discarding 50% of each parent's DNA. After a few generations it becomes increasingly likely that all of a parents' DNA will have been discarded in that family line. That is, eventually, even though one knows of a direct ancestor, none of that ancestors' DNA may appear in one's own DNA! This observation does not of course apply in the case of mitochondrial DNA which is transmitted through the female line, and Y-chromosome DNA which is transmitted through the male line.

Notwithstanding such complications this is an active field of enquiry, and interesting findings have been made. In a recent study a promising genetic signature of Sephardic Jews is examined (ref 305). An earlier result is cited - from which it emerges that the Ashkenasim, which comprise the largest Jewish population worldwide, shows a prominent founder effect with only 4 mitochondrial haplotypes comprising 40% of the modern population and with the most frequent haplotype found in 19% of individuals. Sephardim, descendents from Spanish and Portuguese Jews who were the largest Jewish population until the 18th century, instead show a large variation in maternal founders of the communities of the Ottoman Empire. This was especially apparent in their results for Turkey, with the 4 most frequent haplotypes found in only 17% of the present day descendent population and the most frequent haplotype found in not quite 6% (for Bulgaria, the numbers are 27 and 8.5%, respectively). The Ottoman Empire, including Turkey and Bulgaria, received many of the Jewish people who were exiled from Spain and Portugal in the late 15th century. The contrasting findings for the two prominent Jewish populations suggest a greater genetic diversity in mitochondrial DNA in Sephardim than in Ashkenasim. However it is noted that the seemingly higher genetic variability in the present-day Sephardic population does not preclude uncovering Sephardic signatures, the object of the study.

Our distant cousin Michael Waas has conducted a study of male-line Sephardic descent in which some of us participated (see ref 306). His collaborator Adam Brown in the online discussion group Sephardic Diaspora during 2019 referred to the Ashkenasi founder effect (see above) and the likelihood that Randy Schoenberg (and hence all of us who descend via the Barrows from Simon Michael Pressburg) does not descend from the small number of original founders of the Ashkenasi community. This discussion is ongoing - but perhaps the ancestors of Simon Michael Pressburg included people from the Sephardic Diaspora. In any event, Michael Waas reported on 25 Jan 2020 that in respect of Julian Land 'we do have some very small 3 CM segments shared between us. But who knows if that's from the Portuguese or Ashkenasi sides of our families'.

John Griffiths, descendant of Joseph Barrow, has matched his and Julian Land's DNA data on GEDmatch and noted that we have a 3.4 centiMorgan segment match on our 8th chromosome which would put a common ancestor in the early 1700s. This of course matches our known common ancestors Simon Barrow 1709-1802 and Bailah Montefiore 1720-73. Then, Randy Schoenberg having provided access to his DNA records, John Griffiths and Julian Land found matches with Randy Schoenberg, with one segment match on the 21st chromosome being common to all 3 people, essentially confirming a common ancestor. The failure of this 21st chromosome segment to show up in the comparison between John Griffiths and Julian Land is a puzzle but is currently thought to be an outcome of the way the analysis algorithms interact with shifts in DNA over generations (in autosomal DNA matching - done in this comparison - not every nucleotide position is evaluated but a subset of them. This subset consists of SNPs - or single nucleotide polymorphisms which in the common operational assumption must be possessed by 1% of the population - with an undisclosed but no doubt predetermined level of SNP matching being the criterion for segment matching. Perhaps after many generations SNPs disappear differentially and non-uniformly from the DNA of different descendants, not enough to prevent the 21st chromosome matches with Randy Schoenberg but enough to prevent the mutual match). Nothing needs to be explained in connection with the failure of Randy Schoenberg's DNA to show the 8th chromosome match - this part of his DNA has been effectively discarded. In any case, two things stand out from the 3-way comparison - Julian Land has a stronger link with Randy Schoenberg than does John Griffiths; but John Griffiths has a match with Randy Schoenberg in the absence of a Lyon de Symons connection. Both these observations support our suggestion that the Barrows via Baruch of Livorno have an additional connection with Randy Schoenberg compared with the known Lyon de Symons connection. In addition, an anonymous correspondent found on Family Tree DNA that 'hooray we have the same 5th cousin. I found him in your kit and then went on my cousin's kit .. we both have him....If we both have the same 5th cousin we must be related!' This leads us to suggest here that the de Dirsztay dynasty descends from a brother of Simon Barrow of Barbados namely Gedalia bar Baruch of Prague. Our two suggestions thereby derive support from DNA analysis, and we can now regard Simon Michael Pressburg as a common ancestor of all 4 of us. We await further DNA comparisons from our anonymous correspondent, and others, for any additional light that can be shed.