Book Review: Understanding DNA Ancestry

Understanding DNA Ancestry

By ‎‎Professor Sheldon Krimsky

Published by ‎‎Cambridge University Press

ISBN-10: ‎‎1108816037, ISBN-13: ‎978-1108816038

Buy this book from Amazon UK

Nearly 35 million people around the world have now taken a genetic ancestry test according to the International Society of Genetic Genealogy. These tests provide matches with genetic relatives to help with family history research but also provide a biogeographical ancestry analysis to provide an indication of a person's ancestral origins. The science of ancestry testing is complicated and often misunderstood so there is a great need for resources which provide clear explanations.

Understanding DNA Ancestry by Sheldon Krimsky is part of a series of books published by Cambridge University Press which aims to provide accessible guides on a wide range of subjects to stimulate debate and correct misconceptions. Krimsky's goal in writing the book was to 'decipher the process of DNA ancestry testing and to demystify the elusive technical components'.

Relative matching is the most meaningful and useful component of a genetic ancestry test. With the massive growth of the DNA databases in recent years we've seen how DNA testing can have a disruptive effect on society. People are discovering through DNA that they were adopted or donor conceived and that they have close relatives, such as siblings, whom they knew nothing about.

Those of unknown parentage can take a DNA test to identify their biological parent by working with their cousin matches and building out family trees. The fertility sector is having to come to terms with the fact that DNA testing has effectively ended donor anonymity (see BioNews 939). The same methods used by adoptees and donor-conceived individuals to identify biological parents are now being used by law enforcement in the USA and a few other countries to solve cold cases. Krimsky covers these important issues briefly in two chapters in the book. However, the methodology for performing the relative matching is covered in just a few short and inadequate paragraphs with specific reference to the third-party website GEDmatch, the main site used for the law enforcement cases. The methods used by the major genetic ancestry companies such as AncestryDNA and 23andMe to detect relatives and predict relationships are not discussed at all.

Rather than focusing on these practical applications of genetic ancestry testing, the bulk of the book is concerned with the methods used to provide biogeographical ancestry reports. Early attempts to infer ancestral origins used a very limited panel of a few hundred or few thousand so-called 'ancestry informative markers' (AIMS). These are single nucleotide polymorphisms (SNPs) which were identified as being more prevalent in certain populations than in others. These tests could provide only broad continental-level assignments.

Since 2007 the major testing companies have been using off-the-peg genotyping microarrays (chips) which cover between 650,000 and one million markers scattered across the entire genome. A subset of around 300,000 markers is generally used to provide the biogeographical ancestry report when people purchase these home ancestry tests. The companies each have their own reference populations comprised of publicly available datasets combined with samples from customers with known ancestry from specific regions or countries of interest. Each company has its own proprietary set of algorithms for defining the populations and estimating ancestry. Rather than identifying individual AIMS, most of the companies now leverage the power of markers linked together in short segments which are then compared with the reference populations.

Krimsky discusses older methods of ancestry inference based on allele frequencies and AIMS but provides little insight into the current methods used by the testing companies. The explanations are often confusing and sometimes incorrect. For example, the author suggests that AncestryDNA tries to identify SNP panels for different populations whereas the white paper he cites explains how the reference populations are sorted into geographical clusters based on a technique known as principal components analysis.

The science has moved on in recent years and more accurate methods of inferring recent ancestry are now available. AncestryDNA introduced a feature called Genetic Communities in 2017 which provides detailed subregional assignments. The communities are based on genetic networks of cousins sharing sizeable chunks of DNA. The family trees of the people in the network are then investigated to identify shared locations in their family trees. The methodology was published in a peer-reviewed scientific paper published in Nature Communications and in an associated white paper by AncestryDNA. AncestryDNA can now place people in over 1500 specific sub-regions which reflect their recent ancestry within the last 200-300 years with remarkable accuracy. MyHeritage launched a similar feature known as Genetic Groups in 2020. These features are however not discussed at all in the book.

The book contains a few unfortunate errors. AncestryDNA was not an offshoot of National Geographic and although they briefly offered a health test it was suspended in January 2021. FamilyTreeDNA (abbreviated as FTDNA not FTD) was one of two companies which began offering DNA testing in the same month in 2000, the other being Oxford Ancestors which is now defunct.

Unfortunately I do not think this book achieves what it sets out to do and it will only serve to add to the public confusion. There are a number of genetic genealogy textbooks which provide a much better introduction to DNA ancestry testing such as The Family Tree Guide to DNA Testing and Genetic Genealogy by Blaine Bettinger and Tracing Your Ancestors Using DNA edited by Graham Holton. These books emphasise that the biogeographical ancestry reports are only a small component of a DNA test. If you really want to find out about your ancestry you need to do some genealogical research. DNA testing is a useful tool to help with that research and can provide clues to ancestral origins but it cannot provide all the answers.

Buy Understanding DNA Ancestry from Amazon UK.