52 Ancestors in 52 Weeks became a bit onerous for me to keep active for a variety of reasons and it has been a few months since my last blog. One of the primary reasons was my decision to only write about people who are no longer living and to also write about topics that would not affect family and friends who are living. I soon realized I did not have enough stories that would fulfil these criteria.
A new year has begun and I am starting over. My new goal will be a little more fluid and my expectations are to write a blog about a topic of my current genealogical interest and may not necessarily be a weekly entry.
Over the last few years I have seen many advertisements by genealogical DNA testing companies that market they can build your ethnicity report and you will find out where your ancestors came from. I have also seen postings on social media stating ‘DNA is a scam’. Some media outlets have written articles or aired documentaries stating similar findings.
These statements and/or reports are only partially true and they lead to misinformation and misunderstanding of genealogical DNA tests. These tests provide two reports to the consumers; an ethnicity report, as documented by scientists, the media and others as inaccurate, and DNA matches to relatives, which genealogists and researchers find fairly accurate.
As a result of the advertisements, DNA testing is no longer just an interest for genealogists to further their family tree research or for adoptees to search for their biological families. It has become a mass consumer market with a large number of participants wanting only to find out where they came from. It is estimated that more than 12 million people have their DNA samples in the database of the five major genetic testing companies: Ancestry DNA, 23andMe, Family Tree DNA, Living DNA and My Heritage DNA.
We all have DNA we have inherited from our ancestors as it is passed on from generation to generation. The passing on of DNA from a parent to a child is somewhat by chance as siblings will not inherit the exact DNA from their parents unless they are identical twins/triplets/etc.
Each parent provides 23 chromosomes to their child; 22 autosomal chromosomes and 1 sex chromosome. These chromosomes are not passed on intact to their children because a parent only passes on half of their DNA and it is a mixture or recombination of the DNA they inherited from both of their parents. DNA recombination is the exchange of DNA strands from the parents’ chromosomes by breaking and rejoining DNA segments. This creates a new genetic combination which allows for genetic diversity and only half of this is passed on from each parent to a child.
Siblings share about 50% of their DNA. As a result of the recombination siblings don’t inherit the exact same DNA mix from their parents (unless they are identical twins, triplets, etc.). This DNA recombination occurs with every generation and leads to distant cousins inheriting completely different DNA from their ancestors and the more distant the relative is the more likely there is no DNA shared between them. It is estimated that about 10% of third cousins (share the same great-great-grandparents) and 45% of fourth cousins (share the same great-great-great-grandparents) do not have any matching DNA.
DNA apparently doesn’t replicate perfectly. It is estimated that every generation creates about 100 new mutations (SNPs). Most of these are harmless and about half of them get passed from the parent to the child in each generation. This means that you may have about 100 SNPs that are unique to you, as well as, about 50 that are unique to each of your parents, about 25 that are unique to each of your grandparents, about 12 that are unique to each of your great-grandparents and so on. The last four generations of your family have provided you with about 400 SNPs in your DNA that are unique to your family. Your siblings share some of these SNPs, but because of your DNA recombination they will not share all of them; they will have their own unique SNPs and a different combination of them from your parents.
As every generation passes only 50% of their inherited DNA then it doesn’t take many generations before descendants have inherited only a little. A simple diagram to describe this is shown below.
As a result of culture, ethnicity, geography, religion, socio-economics, or tribal groups some people have a limited group to marry within resulting in an endogamous population (everyone descends from the same small gene pool). Children born of these unions will inherit some identical SNPs from both parents resulting in them having two copies of the same SNPs. This would guarantee their children would also carry these SNPs. This practice leads to these SNPs becoming fixed in that population which means every member of that population would have these SNPs. This combination of SNPs would be unique to that lineage. The interpretation of autosomal DNA matches within this population would be deceiving because people will be related to each other on multiple ancestral pathways and the same ancestor will appear in many different places on the pedigree chart resulting in the fact the relationship will be more distant than the DNA match suggests.
When a population is confined in the same geographic location for a long time SNPs become fixed; this is called genetic drift. Some of these fixed SNPs might alter hair colour, eye colour, skin tone or bone structure as the result of particular genes that disappear when individuals who carry them die or do not reproduce. It will take the combined effort of many hundreds of SNPs to produce the characteristics of individuals we label a “race” because all the members would share some SNPs that are considered unique to that genetic race (genotype). The interaction of genotypes within their environment leads to observable characteristics of an individual and the social construction of race (phenotype).
The phenotype is also tied to culture (Scottish being different than Irish), while the genotype is tied to geography (SNPs that are unique within a population from a certain area, such as, Scottish and Irish ancestry tend to be called Scotch-Irish, as it’s hard to distinguish the two, genetically).
Scientist have sequenced the DNA of many cultures and geographic locations around the world. One of the ways scientists confirm their pool of DNA has adequately represented the place they are testing is they require the pool (the reference population), to have four grandparents born in that location. Some scientists feel they have enough information from these various reference populations to identify which unique SNPs are associated with a geographical region. These scientists also feel by calculating the percentage of unique SNPs that you share with the current population of a geographic location, they can determine whether you inherited those SNPs from a parent, grandparent, great-grandparent, etc. When scientists take the sum total of all your SNPs and compare them to genetic databases they believe they are able to compute your overall racial composition.
There are different types of DNA used during analysis for genetic testing; Y chromosome DNA, mitochondrial DNA or autosomal DNA. Y chromosome DNA (Y-DNA) traces a man’s paternal line. Mitochondrial DNA (MtDNA) traces the maternal line as people inherit mitochondria only from their mothers. Neither of these DNA types change very much over time and, as a result, do not provide much information about recent ancestors. Autosomal DNA (AtDNA) is inherited from autosomal chromosomes of which we have 22 pairs. AtDNA testing looks for genetic differences on all of the chromosomes except the X and Y sex chromosomes and is the type most used for genealogical purposes as it is a mix of both your parents.
To produce a report, companies use equipment to sequence the DNA to determine the order of nucleotides which more specifically means the order of four amino acid bases: adenine, guanine, cytosine and thymine which in doubled stranded DNA are linked in a paired configuration. The equipment used contains chips that determine which SNP location is tested and different chip versions are used by different testing companies. Once the base pair identification has been completed on your DNA sample the testing company will check it against the samples they have in their database.
The ‘DNA match to relatives’ report one receives from the various testing companies will compare your overall SNP pattern with those of others in their database and will show who you are related to, but it does not show you which side of your family the match comes from. AtDNA tests can confirm matches to relatives with a high level of accuracy in the last 5 – 6 generations. The distance a match relates to you is based on the percentage of shared DNA.
Most companies use an algorithm that looks for shared consecutive SNPs (called a segment match). A segment match of at least 7 – 10 centimorgans is considered notable. Centimorgans (cMs) are the units used to measure genetic distance. There are about 1 million base pairs in a centimorgan. Most testing companies will show you the number of cMs you share and across how many segments. The higher the number of shared cMs the closer the relative the match is.
Some testing companies provide chromosome browsers which allow a tester to view which chromosome they match with another, as well as, the number and length of matching segments on the chromosome. When comparing multiple matches, you may notice these segments overlap with more than one person at the same spot. This is called triangulation and suggests you share the same ancestor. You can also download your ‘raw data’ from your testing company and upload it to GEDmatch, an open data personal genomics database and genealogy website, and use their chromosome browser or other genealogical analysis tools.
The ethnicity report one receives from the various testing companies is only an estimate. To produce the ‘ethnic makeup report’, a company will compare your overall SNP pattern to those of people from particular geographic locations. Some of the companies draw their reference population DNA samples from public databases compiled by the 1000 Genomes Project, a catalog of human genetic variation of people around the world, as well as, from other studies. Many of these companies broaden their databases by increasing information from particular parts of the world by testing more people. Each testing company uses its own proprietary database of DNA samples called ancestry informative markers (AIMs). This means the testing companies do not use the same reference populations and this leads to the difference in the reports you receive from one company to the next.
The companies use common genetic variations as the basis for estimating the probability of your ethnicity. One company may report that you have 50% of your DNA from North Europe, 30% from Asia, 10% from Eastern Europe and Russia and 10% from Greece and the Balkans, based on their method used to compare to the information in its database. Another company has their own database and they may report the probability is that you have 40% of your DNA from North Europe, 40% from Asia and 20% from Eastern Europe and Russia. The ethnicity report is based on who they do and do not have in their database.
For companies to be able to provide information on which country, or more specifically, which part of a country your ancestors came from, they will require sampling many people in those countries, along with a more complicated math or algorithm to detect the slight differences in the patterns.
Direct-to-consumer DNA testing for genealogical purposes has been a controversial subject since it first became available in about 1998 from the now defunct company, GeneTree.
In January 2018, Sheldon Krimsky, the Lenore Stern Professor of Humanities and Social Sciences and an adjunct professor in public health and community medicine at Tufts, stated “Companies selling these services don’t share their data, and their methods are not validated by an independent group of scientists.” He goes on to say, “Studies that have compared ancestry databases have found poorer concordance with Hispanic, East Asian and South Asian descent. There’s a big chunk of data — actually the majority — that these genetics-testing services don’t use. Your DNA contains millions of SNPs, but these tests are selectively looking at certain genetic variations and use between 100 to 300 AIMs, which account for a small part of the SNPs that differentiate the human family. So even if a test says you are 50% European, really it can only report that half of those SNPs of your DNA looks to be European. The results are further skewed by the fact that certain ancestry information markers used by any particular test may come from only your paternal line (Y chromosome) or your maternal line (mitochondrial DNA). Tests using these markers are less accurate. Finally, these testing services use DNA from modern populations in these regions to draw conclusions about people who lived in those areas hundreds or thousands of years ago. It’s a big leap to assume that the particular SNPs used by the tests have remained constant for all that time.”
Companies that sell genealogical DNA tests advertise they can provide your ethnicity report and you will find out where your ancestors came from. Many scientists say these results are beyond the capabilities of the test, such as, Deborah Bolnick of the University of Texas in Austin in October 2007 when she stated “But they’re not going to tell you every place or every group in the world where people share your DNA. Nor will they necessarily be able to tell you exactly where your ancestors lived or [what race or social group] they identified with.” Deborah went on to say “Present-day patterns of residence are rarely identical to what existed in the past, and social groups have changed over time, in name and composition.
In June 2018, Deborah Bolnick stated, “They [DNA testing companies] present these very specific, precise numbers down to the decimal point. But it’s false precisions. In reality, what the companies can say with certainty is that you share common DNA patterns with people living in those places today. But your ancestors may not always have lived where their descendants do now. People move around which muddies the waters. Take a stretch of DNA containing a particular SNP pattern. Today it may be found in the US and in relatives in England and Germany, but it could be that 500 years ago your shared ancestor lived in Italy. Going further back in time, that stretch of DNA may look like it came from Romania, Mongolia and Siberia. As people move and the genes they have moved with them, it’s going to change what those geographic ancestries look like. Further complicating matters, most people think of their ancestry as coming from particular countries, but genetics cuts across and transcends national borders. In reality those categories are not genetic, they’re sociopolitical and historic.”
Drew Smith, a genealogical librarian at the University of South Florida in Tampa agrees and in June 2018 stated, “From a DNA perspective, it’s hard to tell a French person from a German person.”
Another area of concern of many scientists is the poor DNA representations of various groups in these reference population databases. In April 2018, Krystal Tsosie, a geneticist at Vanderbilt University in Nashville stated, “And some groups, including aboriginal populations in Australia and big parts of Africa and Asia, are mostly absent from companies’ databases. The same goes for Native Americans, whose samples in public databases are small, and in some cases, were collected by questionable means.” Krystal goes on to say, “As a result of mistrust of genetic research, there are not enough people from the 566 federally recognized tribes in the genetic databases to enable customers to learn about their tribal heritage from DNA tests. And even if a DNA test could establish that a person carries DNA inherited from a Native American ancestor, that doesn’t make that person a member of the tribe.Tribal memberships are based on family and community ties, not DNA”
In an article written by Nicholas Anthony in April 2018 he states, “It’s going to get a lot harder with future generations now that airplanes exist. Most of the SNPs in today’s races became fixed due to long periods of geographical stability. People didn’t move around all that much, and when they did, it was usually only a handful of families that moved to a new location, bringing with them a set of unique SNPs that soon became fixed in that new location due to the founder effect. But now that travel is easy and mass migrations are occurring due to war, famine, and the promise of a better life, future geneticists are going to have a hard time placing your lineage geographically. They might be able to say whether a great, great, great grandparent was an Ashkenazi Jew, but the more recent generations will be difficult to pin down.”
Genealogical DNA tests analyze less than 1% of a person’s DNA and this may result in missing most of one’s relatives. As the cost of DNA testing decreases the prospect of whole gene sequencing may arrive soon. DNA testing is both inaccurate and accurate depending on which report you are looking at.
Some of the testing companies are using advertisements to promote the sale of the testing kits. Recently, there appears to be more of an emphasis in these ads to use the ethnicity reports as the reason one might want to buy a kit. One such ad is from Ancestry DNA and it features Kyle Merker, who says he grew up thinking his ancestors came from Germany. In the ad he states he danced in German folk groups and wore lederhosen. He goes on to say his DNA results showed 52% of his DNA came from Scotland and Ireland and that he swapped his lederhosen for a kilt. This ad leads you to believe it was because of the DNA results that caused Kyle to change his culture. This, apparently, was not the case as an article about Kyle was published in the Parade, April 29, 2016 and documents he researched his family through newspaper articles and government records. It was these traditional genealogical resources that really told Kyle about his family’s stories and this was only supported by his DNA results.
As stated earlier some media outlets have reported on the lack of accuracy of DNA testing. One such report wasa recent CBC Marketplace aired episode titled “DNA Ancestry Tests: Can You Trust The Results” with the description ‘Marketplace investigates the science and marketing behind popular DNA Ancestry kits. Just how accurate are they? Are ancestry DNA tests 100% accurate? Charlsie Agro tests 5 top brands…and we’re sending in the saliva of her identical twin sister too.’ The report leads you to believe DNA testing is not accurate. However, this report focused solely on the ethnicity report and did not provide any information about the DNA matches to relatives that you also receive. As a result, this investigative report was misleading in its conclusions.
Ethnicity is based on more than just DNA. The border of countries has changed many times in the history of humans, as well as the mixing of what we call “races”. Ethnicity is a concept and it is fluid. DNA tests cannot account for the recent migrations of peoples from their ancient homelands. For these reasons, the ethnicity reports you receive have a greater confidence level when they provide a more general report on a broad continental scale. When companies start focusing at a county level the confidence of these reports drop.
DNA match to relativesis used more and more by genealogists in their research. The accuracy of these matches is determined by the number of shared centimorgans. According to Blaine Bettinger, The Genetic Genealogist, a 15 cM or higher match will have a 99.3% probability that it matches one of your parents and it drops to a 94% probability with a 10 cM match. These matches can help breakdown brickwalls in your paper research, support the genealogy discoveries you have made and help find biological family for individuals looking for their birth parents.
DNA is part of everyone and if you feel this is an important part of you, then start working on your own genealogy. Take a DNA test, create a tree and enter the information you have on your relatives, both living and dead. Look at how you can fit the DNA matches into your tree or connect with them to expand a branch of your tree.
Most importantly, start researching for documents (birth, death, marriage, military, and census records, etc.). This will allow you to capture accurate information and the stories about individuals; where they were born, married or died, where they lived and worked, who their parents and siblings were, etc. It will also allow you to expand your tree further back to older generations and down the lines of descent of the other branches of relatives. To really confirm your heritage, you need to follow the paper trails. DNA is just another type of record that can add and support your information.
As stated by Krystal Tsosie, a geneticist at Vanderbilt University in Nashville. ‘Our character, who we are, who we come from is a complex story of a variety of nonbiological factors. To reduce that to a test kit is actually going to ignore the beauty and complexity that is us.”
Citations
N. Anthony. How is a DNA test able to determine ethnic background? Quora. Pub. 23 April 2017.
G. Rajewski. Pulling Back the Curtain on DNA Ancestry Tests. TuftsNow. Pub. 26 January 2018.
T.H. Saey. DNA testing can bring families together, but gives mixed answers on ethnicity. Science News. Pub. Vol. 193, No. 11, June 23, 2018, p. 14.
T.H. Saey. Consumer DNA testing promises more than it delivers. Science News. Pub. Vol. 193, No. 9, May 26, 2018, p. 20.
K. Than. Genetic Ancestry Tests Mostly Hype. Live Science. Online pub. 18 October 2007 10:00am ET.