CHRIS POMERY'S DNA PORTAL
1. DNA & the Family Historian
DNA testing is now establishing itself as the third, and newest, core source in the field of family history, supplementing knowledge gained from oral and documentary records. While the convergence of genetics & genealogy into a new science called 'genetic genealogy' is some way off, DNA tests by one-name groups in the UK and the USA are already revealing valuable and challenging results. The pages accessed via this portal summarise the main developments in the field of DNA testing that are of most relevance to family historians. I expect that within a couple of years the price of DNA testing for family historians will have fallen sufficiently for it to have become a mainstream activity for most one-namers.
1.1. DNA tests available to the Family Historian
There are two basic DNA tests being offered to family historians: the Y-chromosome test and the mitochondrial test. The Y-chromosome in the nuclear DNA of every living man resembles that of his father and his paternal grandfather, and is carried by male cousins of any degree that share the same male ancestor. Tests of tiny chemical markers in one part of the Y-chromosome that does not change much over time will reveal the testee's haplogroup, one of 28 shared by all humans on the planet. Tests of other markers in another part of the Y-chromosome that changes more rapidly reveal the testee's haplotype, the numeric pattern of their individual DNA. Combined together the two tests distinguish one male-to-male lineage from another and reveal a 'DNA signature' for each individual man. The mitochondrial test looks at the mitochondria, a special part of nearly all human cells, which is passed on female-to-child and is inherited down the female line. It is generally used to study long-term population developments such as migrations and has no real use for family historians. The Y-chromosome test can only be taken by men while the mitochondrial test can be taken by both men and women.Click here for links to background information on the science of DNA testing and genetics, including a glossary, which will help you understand terms found on these pages.
What DNA tests can show
The tests can be applied to link specific individuals, or to build up the picture of the ancestry of people sharing the same name, or to map the genetic orgins of large segments of the population.The Y-chromosome test (the Y-test) can indicate:
- whether specific individual men share a common male ancestor.
- if a set of men with the same or similar surname are directly related through a common ancestor.
- how many different common male ancestors any given group collectively shares.
- to which broad haplogroup each individual male belongs to (for example, over half of all Europeans belong to one of two major haplogroups of 28 known worldwide).
- an analysis of the mutations in the Y-chromosome can also be used to estimate the degree of separation between individual males in terms of the number of generations since the separation occurred. That man is often referred to as the most recent comon ancestor or MRCA. (There is currently a debate over the 'natural' rate of mutation of individual DNA markers over time.)
- reveals details about the distant origins of maternal ancestors.
- can be used to link individuals via the direct female line (i.e. mother-to-mother).
Results from Y-chromosome tests within groups sharing the same or related surnames are yielding the most interesting results for family historians to date:
- holders of surnames that are rare, relatively well-spread or relatively common have labelled the genetic identity of a single common ancestor, and if there is no single ancestor have begun to work out how many ancestors might have taken the name 500-800 years ago when the male-to-male hereditary naming practice began in England.
- names that appear to link to a known single common ancestor have been able to prove that connection
- names that have several documented lines inter-connecting in the same geographical location are using DNA testing to unravel them.
- holders of a name living in the New World are being able to prove a genetic link with others in the Old World of Europe.
- members of different surname suspected of being linked to a one-name group have been tested in order to confirm this hypothesis.
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1.2. Overview of existing surname-based Y-chromosome DNA test projects
Close on 150 Y-chromosome test projects have so far been announced by one-name groups worldwide.A comprehensive list of completed, ongoing & proposed tests is maintained here on this site.
Please Email me if you know of one that is not on this list!
Modelling the distribution of haplotypes and surnames
Academics are now focusing on using genetic data to define different models for surname development and the modern distribution of surnames and haplotypes. The best paper on this is Mark Jobling's 'In the name of the father: surnames and genetics' published in the June 2001 edition of Trends in Genetics. Here he outlines four scenarios to describe the hypothetical relationships between three surnames using the main variables governing the fidelity of DNA transmission across the generations, namely the number of men originally with a given surname and the year of the single common ancestor. One would expect that most surnames would look more or less like one of these scenarios, but so few tests have been done on one-name groups that there's too little data to demonstrate it yet. Logic might suggest that surnames in a single country with a low modern male population are more likely to show a single common ancestor than surnames with large modern male populations, though where the boundary is between a rare and common surname can only be guessed. It is quite feasible to imagine that some major surnames have a single or few founders and others have multiple founders.Investigating migration within a country
The Pomeroy study attempts to cross-reference the DNA results against a documentary history of every person with that surname in the UK. The results show that all families of Cornish origin have closely-related, but slightly different, DNA signatures. (To understand how this conclusion was reached it is best to read the whole study through from the beginning.) Documentary studies had already shown Pomeroy researchers that the greatest dispersal of the name away from its west country roots has occurred since 1870 and that the modern distribution pattern is quite different from the historical one. It may be that other names, like Savin, for example, have undergone relatively little geographical dispersion and retain to modern times their long-standing regional allegiances which are confirmed in the DNA test results; or it may be that the relative lack of geographical dispersal is an inherent feature of some one-name groups.Linking variant surname spellings
Surname spellings are not necessarily indicators of unique genetic origins. Both the Mumma and Pomeroy surveys found mixes of variant surnames in different DNA-related groups. In some cases a particular spelling variant has been shown through DNA analysis to be unrelated to any other variant in any way. The Pomeroy study found that certain surname variants occurred in only one haplogroup and had their origins in fewer geographical locations.Return to top of page
1.3. Representing the results of DNA studies
Y-chromosome test results are complex and demand new ways of representing them in a simple format. The most comprehensive explanation done to date is on the Mumma website which shows raw results in a standard spreadsheet-type format, then re-arranged by ancestor as derived from documentary evidence, and finally in pedigree charts that show the number of generations from specific ancestors to the present day and how the testees link to them. The explanation of the results is excellent. The Stiddem study also uses pedigree charts to clarify its results as does the Dooley study which shows how individual testees in six DNA-defined haplotypes link back in a common ancestry as researched by traditional documentary means.The Walker study shows personal details for each generation of each descendent group in their tests, which allows readers to visually identify particular families and their histories. The Duerinck study shows how the spreadsheet format can quickly illustrate linkages between different surnames in the same study.
My own website uses phylogenetic network software to reveal new levels of data within the results. The basic chart is created by the software to indicate the number of mutational steps between individual samples. On top of this I have added numbers derived from our documentary research to cross-reference the Pomeroy results for testees in the main haplogroup to show the number of testees per haplotype, the total number of adult males per haplotype, the total number of Pomeroys known to be linked in the documentary history of these families, and finally the different 'ancestral groups' revealed by the test programme. Another chart shows the geographic origins of the oldest known members of testees' families, a format which reveals some eye-catching results.
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1.4. Key questions & issues thrown up DNA testing
In the DNA testing of males in a one-name group, two key questions dominate the analysis of the results:- what is the likelihood of a direct male to male transmission of DNA being uninterrupted at some point across a large number of generations, and what reasons are there for a break occurring?
- what is the standard rate of mutation of the Y-Chromosome which, once known, would allow us to estimate how long ago two almost identical DNA signatures with, say, a single-step or double-step mutation difference, diverged from their common haplotype? In other words, is there an accurate way to calculate how long ago the most recent common ancestor lived when two DNA signature are almost, but not quite, identical?
Reasons for a break in male DNA transmission
There are five main scenarios to explain a break in the male to male transmission of a DNA signature within a particular family tree traced back from modern times:- a male child was born illegitimately to an unmarried woman and kept her surname when he grew up, perhaps being passed off as her brother
- a male child was fathered illegitimately within a marriage, with or without the legal husband's knowledge and where the child kept his surname
- a husband marrying a woman with the surname who adopts it upon his marriage rather than retaining his own surname, and/or the children of this 'female line' adopting their maternal grandfather's name, most likely to secure an inheritance or as a conscious decision
- children born within another marriage adopt their stepfather's surname on their mother's re-marriage and thus switch surname
- a family adopts a male child who takes their surname
- upon naturalisation a foreign name is altered to resemble an existing local surname
- a male purchaser of property adopts the surname of the seller when buying an important estate
- there is a mis-spelling at some point in history that switches an individual or a family to a new surname group entirely
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1.5. Monitoring developments in the field of DNA testing
If you want to monitor developments in genetic testing relating to family historians you can subscribe to the Genealogy-DNA mailing list. The list archives began in October 2000.The following books, pamphlets and reprints can be used to read up on the subject offline:
- How to DNA Test Our Family Relationships?, by Terrence Carmichael and Alexander Kuklin, ISBN: 0-9664027-1-5
- The Seven Daughters of Eve: The Science That Reveals Our Genetic Ancestry, by Bryan Sykes, W. W. Norton, ISBN: 0-3930201-8-5
- DNA for Family Historians, by Alan Savin, ISBN 0-9539171-0-X (available only direct from Alan)
- The US News & World Report has a well-written feature article that provides an overview for the general reader with lots of links. The June 2000 issue of the National Genealogical Society Quarterly (Vol 88 #2) had an excellent article by Thomas Roderick called The Y Chromosome in Genealogical Research: From Their Ys a Father Knows His Own Son. (A copy is $6.00 plus $2.00 shipping in the USA for the first copy, add $1.00 for each additional copy. Contact the NGS Bookstore, 4527 17th Street North, Arlington, VA 22207. Visa or Master Card accepted.)
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GO NEXT TO: 2. List of Y-Chromosome DNA Studies underway by Family Historians
All corrections & updates should be sent to the page maintainer: Chris Pomery
Last updated: 19th July 2002. Page launched: 2nd March 2001.
