Genetic genealogy is the use of genealogical DNA tests, i.e.,

DNA profiling DNA profiling (also called DNA fingerprinting) is the process of determining an individual's DNA characteristics. DNA analysis intended to identify a species, rather than an individual, is called DNA barcoding. DNA profiling is a forensic tec ...

and

DNA testing Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, ...

, in combination with traditional genealogical methods, to infer genetic relationships between individuals. This application of genetics came to be used by family historians in the 21st century, as DNA tests became affordable. The tests have been promoted by amateur groups, such as surname study groups or regional genealogical groups, as well as research projects such as the Genographic Project. As of 2019, about 30 million people had been tested. As the field developed, the aims of practitioners broadened, with many seeking knowledge of their ancestry beyond the recent centuries, for which traditional pedigrees can be constructed.

History

The investigation of surnames in genetics can be said to go back to George Darwin, a son of

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...

and Charles' first cousin

Emma Darwin Emma Darwin (; 2 May 1808 – 2 October 1896) was an English woman who was the wife and first cousin of Charles Darwin. They were married on 29 January 1839 and were the parents of ten children, seven of whom survived to adulthood. Early lif ...

. In 1875, George Darwin used surnames to estimate the frequency of first-cousin marriages and calculated the expected incidence of marriage between people of the same surname ( isonymy). He arrived at a figure of 1.5% for cousin-marriage in the population of London, higher (3%-3.5%) among the upper classes and lower (2.25%) among the general rural population.

Surname studies

A famous study in 1998 examined the lineage of descendants of Thomas Jefferson’s paternal line and male lineage descendants of the freed slave Sally Hemings.

Bryan Sykes Bryan Clifford Sykes (9 September 1947 – 10 December 2020) was a British geneticist and science writer who was a Fellow of Wolfson College and Emeritus Professor of human genetics at the University of Oxford.Oxford University, tested the new methodology in general surname research. His study of the Sykes surname, published in 2000, obtained results by looking at four STR markers on the male chromosome. It pointed the way to genetics becoming a valuable assistant in the service of

genealogy Genealogy () is the study of families, family history, and the tracing of their lineages. Genealogists use oral interviews, historical records, genetic analysis, and other records to obtain information about a family and to demonstrate kinsh ...

and history.

Direct-to-consumer DNA testing

In 2000,

Family Tree DNA FamilyTreeDNA is a division of Gene by Gene, a commercial genetic testing company based in Houston, Texas. FamilyTreeDNA offers analysis of autosomal DNA, Y-DNA, and mitochondrial DNA to individuals for genealogical purpose. With a database of m ...

was the first company to provide

direct-to-consumer genetic testing Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...

for genealogy research. It initially offered eleven-marker Y-chromosome STR tests and HVR1 mitochondrial DNA tests but not multi-generational genealogy tests. In 2001, GeneTree was acquired by

Sorenson Molecular Genealogy Foundation The Sorenson Molecular Genealogy Foundation (SMGF) was an independent DNA and genealogical research institution with the goal of demonstrating how the peoples of the world are related. SMGF collected DNA samples and genealogical information from i ...

(SMGF), which provided free

Y-chromosome The Y chromosome is one of two sex chromosomes ( allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or abs ...

and mitochondrial DNA (mtDNA) tests. GeneTree later returned to genetic testing in conjunction with its Sorenson parent company until it was acquired by Ancestry.com in 2012. In 2007,

23andMe 23andMe Holding Co. is a publicly held personal genomics and biotechnology company based in South San Francisco, California. It is best known for providing a direct-to-consumer genetic testing service in which customers provide a saliva sample t ...

was the first company to offer

saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be ...

-based direct-to-consumer testing, and the first to use autosomal DNA for ancestry testing. An

autosome An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosomes ...

is one of the 22 chromosomes other than the X or Y chromosomes. They are transmitted from all ancestors in recent generations and so can be used to match with other testers who may be related. Companies were later also able to use this data to estimate how much of each ethnicity a customer has. FamilyTreeDNA entered this market in 2010, followed by AncestryDNA in 2012, and the number of tests grew rapidly. By 2018 autosomal testing had become the predominant type of test, and for many companies the only test they offered.

MyHeritage MyHeritage is an online genealogy platform with web, mobile, and software products and services, introduced by the Israeli company MyHeritage in 2003. Users of the platform can obtain their family trees, upload and browse through photos, and sear ...

launched its testing service in 2016, allowing users to use

cheek swab A buccal swab, also known as buccal smear, is a way to collect DNA from the cells on the inside of a person's cheek. Buccal swabs are a relatively non-invasive way to collect DNA samples for testing. Buccal means ''cheek'' or ''mouth''. It is ver ...

s to collect samples, and introduced new analysis tools in 2019: autoclusters (grouping matches visually into clusters) and family tree theories (suggesting conceivable relations between DNA matches by combining several MyHeritage trees and the Geni global family tree).

Living DNA Living DNA is a UK-based company that specialises in DNA testing and analysis whose head office is in the UK with facilities in the USA and Denmark. The service is to provide deep ancestry details from all around the world, using a unique proc ...

, founded in 2015, uses

SNP chip In molecular biology, SNP array is a type of DNA microarray which is used to detect polymorphisms within a population. A single nucleotide polymorphism (SNP), a variation at a single site in DNA, is the most frequent type of variation in the geno ...

s to provide reports on autosomal ancestry, Y, and mtDNA ancestry. By 2019, the combined total of customers at the four largest companies was 26 million. By August 2019, it was reported that about 30 million people had had their DNA tested for genealogical purposes. GEDmatch said in 2018 that about half of their one million profiles were American. Due to the limited geographical distribution of DNA tests, there is inherent racism in the databases and results. The CEO of 23andME, Anne Wojcicki, said in 2020 that her company is "part of the problem." Experts in genetics and health inequities believe the inherent racism of these DNA analyses can be addressed by building diverse ethnocultural teams and encouraging Black, Indigenous and People of Color to get their DNA tested.

Genetic genealogy revolution

The publication of ''

The Seven Daughters of Eve ''The Seven Daughters of Eve'' is a 2001 semi-fictional book by Bryan Sykes that presents the science of human origin in Africa and their dispersion to a general audience. Sykes explains the principles of genetics and human evolution, the parti ...

'' by Sykes in 2001, which described the seven major haplogroups of European ancestors, helped push personal ancestry testing through DNA tests into wide public notice. With the growing availability and affordability of genealogical DNA testing, genetic genealogy as a field grew rapidly. By 2003, the field of DNA testing of surnames was declared officially to have "arrived" in an article by Jobling and Tyler-Smith in ''Nature Reviews Genetics''. The number of firms offering tests, and the number of consumers ordering them, rose dramatically. In 2018, a paper in '' Science Magazine'' estimated that a DNA genealogy search on anybody of European descent would result in a third cousin or closer match 60% of the time.

Genographic Project

The original Genographic Project was a five-year research study launched in 2005 by the National Geographic Society and IBM, in partnership with the University of Arizona and Family Tree DNA. Its goals were primarily anthropological. The project announced that by April 2010 it had sold more than 350,000 of its public participation testing kits, which test the general public for either twelve STR markers on the Y chromosome or mutations on the HVR1 region of the mtDNA. The phase of the project in 2016 was Geno 2.0 Next Generation. As of 2018, almost one-million participants in over 140 countries had joined the project.

Typical customers and interest groups

Genetic genealogy has enabled groups of people to trace their ancestry even though they are not able to use conventional genealogical techniques. This may be because they do not know one or both of their birth parents or because conventional genealogical records have been lost, destroyed or never existed. These groups include adoptees, foundlings, Holocaust survivors, GI babies, child migrants, descendants of children from orphan trains and people with slave ancestry. The earliest test takers were customers most often those who started with a Y-chromosome test to determine their father's paternal ancestry. These men often took part in surname projects. The first phase of the Genographic Project brought new participants into genetic genealogy. Those who tested were as likely to be interested in direct maternal heritage as their paternal. The number of those taking mtDNA tests increased. The introduction of autosomal SNP tests based on microarray chip technology changed the demographics. Women were as likely as men to test themselves.

Citizen science and ISOGG

Members of the genetic genealogy community have been credited with making useful contributions to knowledge in the field, an example of

citizen science Citizen science (CS) (similar to community science, crowd science, crowd-sourced science, civic science, participatory monitoring, or volunteer monitoring) is scientific research conducted with participation from the public (who are sometimes re ...

. One of the earliest interest groups to emerge was the

International Society of Genetic Genealogy The International Society of Genetic Genealogy (ISOGG) is an independent non-commercial nonprofit organization of genetic genealogists run by volunteers. It was founded by a group of surname DNA project administrators in 2005 to promote DNA tes ...

(ISOGG). Their stated goal is to promote DNA testing for genealogy. Members advocate the use of genetics in genealogical research and the group facilitates networking among genetic genealogists. Since 2006 ISOGG has maintained the regularly updated ISOGG Y-chromosome

phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

. ISOGG aims to keep the tree as up-to-date as possible, incorporating new SNPs. However, the tree has been described by academics as not completely academically verified, phylogenetic trees of Y chromosome haplogroups.

Uses

Direct maternal lineages

mtDNA testing involves sequencing at least part of the mitochondria. The mitochondria is transmitted from mother to child, and so can reveal information about the direct maternal line. When two individuals have matching or near mitochondria, it can be inferred that they share a common maternal-line ancestor at some point in the recent past.

Direct paternal lineages

Y-Chromosome DNA (Y-DNA) testing involves

short tandem repeat A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. ...

(STR) and, sometimes, single nucleotide polymorphism (SNP) testing of the Y-Chromosome, which is present only in males and only reveals information on the strict-paternal line. As with the mitochondria, close matches with individuals indicate a recent common ancestor. Because surnames in many cultures are transmitted down the paternal line, this testing is often used by

surname DNA project A surname DNA project is a genetic genealogy project which uses genealogical DNA tests to trace male lineage. In most cultures, there are few or no matrilineal surnames, or matrinames, so there are still few or no ''matrilineal'' surname projects ...

Pedigree family trees

Pedigree

family tree A family tree, also called a genealogy or a pedigree chart, is a chart representing family relationships in a conventional tree structure. More detailed family trees, used in medicine and social work, are known as genograms. Representations o ...

s have traditionally been prepared from

recollection Recall in memory refers to the mental process of retrieval of information from the past. Along with encoding and storage, it is one of the three core processes of memory. There are three main types of recall: free recall, cued recall and serial ...

s of individuals about their parents and grandparents. These family trees may be extended if recollections of earlier generations were preserved through oral tradition or written documents. Some genealogists regard oral tradition as myths unless confirmed with written documentation like

birth certificate A birth certificate is a vital record that documents the birth of a person. The term "birth certificate" can refer to either the original document certifying the circumstances of the birth or to a certified copy of or representation of the ensuin ...

marriage certificate A marriage certificate (sometimes: marriage lines) is an official statement that two people are married. In most jurisdictions, a marriage certificate is issued by a government official only after the civil registration of the marriage. In so ...

s, census reports, headstones, or notes in family bibles. Few written records are kept by

illiterate Literacy in its broadest sense describes "particular ways of thinking about and doing reading and writing" with the purpose of understanding or expressing thoughts or ideas in written form in some specific context of use. In other words, huma ...

populations, and many documents have been destroyed by warfare or natural disasters. DNA comparison may offer an alternative means of confirming family relationships of

biological parent A parent is a caregiver of the offspring in their own species. In humans, a parent is the caretaker of a child (where "child" refers to offspring, not necessarily age). A ''biological parent'' is a person whose gamete resulted in a child, a mal ...

s, but may be confused by

adoption Adoption is a process whereby a person assumes the parenting of another, usually a child, from that person's biological or legal parent or parents. Legal adoptions permanently transfer all rights and responsibilities, along with filiation, from ...

or when a mother conceals the identity of the

father A father is the male parent of a child. Besides the paternal bonds of a father to his children, the father may have a parental, legal, and social relationship with the child that carries with it certain rights and obligations. An adoptive fath ...

of her child. While mitochondrial and Y-chromosome DNA matching offer the most definitive confirmation of ancestral relationships, the information from a tested individual is relevant to a decreasing fraction of their ancestors from earlier generations. Potential

ambiguity Ambiguity is the type of meaning in which a phrase, statement or resolution is not explicitly defined, making several interpretations plausible. A common aspect of ambiguity is uncertainty. It is thus an attribute of any idea or statement ...

must be considered when seeking confirmation from comparison of

autosomal DNA An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosomes ...

. The first source of ambiguity arises from the underlying similarity of every individual's DNA sequence. Many short gene segments will be identical by coincidental recombination (Identical by State: IBS) rather than inheritance from a single ancestor (Identical by Descent: IBD). Segments of greater length offer increased confidence of a shared ancestor. A second source of ambiguity results from the

random distribution In probability theory and statistics, a probability distribution is the mathematical function that gives the probabilities of occurrence of different possible outcomes for an experiment. It is a mathematical description of a random phenomenon ...

of genes to each child of a parent. Only identical twins inherit exactly the same gene segments. Although a child inherits exactly half of their DNA from each parent, the percentage inherited from any given ancestor in an earlier generation (with the exception of X chromosome DNA) varies within a

normal distribution In statistics, a normal distribution or Gaussian distribution is a type of continuous probability distribution for a real-valued random variable. The general form of its probability density function is : f(x) = \frac e^ The parameter \mu i ...

around a median value of 100% divided by the number of ancestors in that generation. An individual comparing autosomal DNA with ancestors of successively earlier generations will encounter an increasing number of ancestors from whom they inherited no DNA segments of significant length. Since individuals inherit only a small portion of their DNA from each of their

great-grandparent Grandparents, individually known as grandmother and grandfather, are the parents of a person's father or mother – paternal or maternal. Every sexually-reproducing living organism who is not a genetic chimera has a maximum of four genetic gr ...

cousin Most generally, in the lineal kinship system used in the English-speaking world, a cousin is a type of familial relationship in which two relatives are two or more familial generations away from their most recent common ancestor. Commonly, ...

s descended from the same ancestor may not inherit the same DNA segments from that ancestor. All descendants of the same parent or grandparent, and nearly all descendants of the same great-grandparent, will share gene segments of significant length; but approximately 10% of 3rd cousins, 55% of 4th cousins, 85% of 5th cousins, and more than 95% of more distant cousins will share no gene segments of significant length. Failure to share a gene segment of significant length does not disprove the shared ancestry of a distant cousin. The best autosomal DNA method for confirming ancestry is to compare DNA with known relatives. A more complicated task is using a DNA database to identify previously unknown individuals who share DNA with the individual of interest; and then attempting to find shared ancestors with those individuals. The first problem with the latter procedure involves the relatively poor family history knowledge of most database populations. A significant percentage of individuals in many DNA databases have done DNA testing because they are uncertain of their parentage, and many who confidently identify their parents are unable or unwilling to share information about earlier generations. It may be easier to identify a shared ancestor in the fortunate situation of shared DNA between two individuals with comprehensive family trees, but finding multiple shared ancestors raises the question of from which of those ancestors was the shared segment inherited. Resolving that ambiguity typically requires finding a third individual sharing both the ancestor and the gene segment of interest.

Ancestral origins

A common component of many autosomal tests is a prediction of biogeographical origin, often called ethnicity. A company offering the test uses computer algorithms and calculations to make a prediction of what percentage of an individual's DNA comes from particular ancestral groups. A typical number of populations is at least 20. Despite this aspect of the tests being heavily promoted and advertised, many genetic genealogists have warned consumers that the results may be inaccurate, and at best are only approximate. Modern DNA sequencing has identified various ancestral components in contemporary populations. A number of these genetic elements have

West Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...

n origins. They include the following ancestral components, with their geographical hubs and main associated populations:

Human migration

Genealogical DNA testing methods have been used on a longer time scale to trace human migratory patterns. For example, they determined when the first humans came to North America and what path they followed. For several years, researchers and laboratories from around the world sampled indigenous populations from around the globe in an effort to map historical human migration patterns. The National Geographic Society's Genographic Project aims to map historical human migration patterns by collecting and analyzing DNA samples from over 100,000 people across five continents. The DNA Clans Genetic Ancestry Analysis measures a person's precise genetic connections to indigenous ethnic groups from around the world.

Law enforcement

Law enforcement may use genetic genealogy to track down perpetrators of violent crimes such as murder or sexual assault and they may also use it to identify deceased individuals. Initially genetic genealogy sites

GEDmatch GEDmatch is an online service to compare autosomal DNA data files from different testing companies. The website gained significant media coverage in April 2018 after it was used by law enforcement to identify a suspect in the Golden State Kille ...

and

allowed their

databases In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases span ...

to be used by law enforcement and DNA technology companies to do DNA testing for violent criminal cases and genetic genealogy research at the request of law enforcement. This investigative, or forensic, genetic genealogy technique became popular after the arrest of the alleged

Golden State Killer Joseph James DeAngelo Jr. (born November 8, 1945) is an American serial killer, sex offender, burglar, and former police officer who committed at least 13 murders, 51 rapes, and 120 burglaries across California between 1974 a ...

in 2018, but has received significant backlash from privacy experts. However, in May 2019 GEDmatch made their privacy rules more restrictive, thereby reducing the incentive for law enforcement agencies to use their site. Other sites such as Ancestry.com,

and

have data policies that say that they would not allow their customer data to be used for crime solving without a warrant from law enforcement as they believed it violated users' privacy.

References

External links

Shared cM Project
– how to determine ones relationship based on Centimorgan (cM) values {{Genetics Human population genetics DNA Citizen science