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Genetic genealogy is the use of genealogical DNA tests, i.e., DNA profiling 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 Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar work ...
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
surname In some cultures, a surname, family name, or last name is the portion of one's personal name that indicates one's family, tribe or community. Practices vary by culture. The family name may be placed at either the start of a person's full name ...
s 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 ...
and Charles' first cousin Emma Darwin. 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 Thomas Jefferson (April 13, 1743 – July 4, 1826) was an American statesman, diplomat, lawyer, architect, philosopher, and Founding Fathers of the United States, Founding Father who served as the third president of the United States from 18 ...
’s paternal line and male lineage descendants of the freed slave Sally Hemings. Bryan Sykes, a molecular biologist at
Oxford University Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the ...
, 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 kin ...
and history.


Direct-to-consumer DNA testing

In 2000, Family Tree DNA was the first company to provide direct-to-consumer genetic testing 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 (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 ...
and
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
(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 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 ...
-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 launched its testing service in 2016, allowing users to use cheek swabs 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, founded in 2015, uses SNP chips 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'' 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 The National Geographic Society (NGS), headquartered in Washington, D.C., United States, is one of the largest non-profit scientific and educational organizations in the world. Founded in 1888, its interests include geography, archaeology, ...
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. One of the earliest interest groups to emerge was the International Society of Genetic Genealogy (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 (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 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 ...
s have traditionally been prepared from recollections of individuals about their parents and grandparents. These family trees may be extended if recollections of earlier generations were preserved through
oral tradition Oral tradition, or oral lore, is a form of human communication wherein knowledge, art, ideas and Culture, cultural material is received, preserved, and transmitted orally from one generation to another.Jan Vansina, Vansina, Jan: ''Oral Traditio ...
or written documents. Some genealogists regard oral tradition as
myth Myth is a folklore genre consisting of narratives that play a fundamental role in a society, such as foundational tales or origin myths. Since "myth" is widely used to imply that a story is not objectively true, the identification of a narrat ...
s 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 ensui ...
s, marriage certificates,
census A census is the procedure of systematically acquiring, recording and calculating information about the members of a given population. This term is used mostly in connection with national population and housing censuses; other common censuses inc ...
reports,
headstone A headstone, tombstone, or gravestone is a stele or marker, usually stone, that is placed over a grave. It is traditional for burials in the Christian, Jewish, and Muslim religions, among others. In most cases, it has the deceased's name, ...
s, or notes in family bibles. Few written records are kept by illiterate populations, and many documents have been destroyed by
warfare War is an intense armed conflict between states, governments, societies, or paramilitary groups such as mercenaries, insurgents, and militias. It is generally characterized by extreme violence, destruction, and mortality, using regu ...
or
natural disaster A natural disaster is "the negative impact following an actual occurrence of natural hazard in the event that it significantly harms a community". A natural disaster can cause loss of life or damage property, and typically leaves some econ ...
s. 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, fro ...
or when a
mother ] A mother is the female parent of a child. A woman may be considered a mother by virtue of having given birth, by raising a child who may or may not be her biological offspring, or by supplying her ovum for fertilisation in the case of ...
conceals the identity of the father 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 twin Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of TwinLast Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two ...
s 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 ...
around a
median In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. For a data set, it may be thought of as "the middle" value. The basic f ...
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-grandparents,
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 DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. T ...
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 and Family Tree DNA allowed their databases 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 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, 23andMe and MyHeritage 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.


See also

*
Allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...
*
Allele frequency Allele frequency, or gene frequency, is the relative frequency of an allele (variant of a gene) at a particular locus in a population, expressed as a fraction or percentage. Specifically, it is the fraction of all chromosomes in the population tha ...
* Electropherogram *
Genetic recombination Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryo ...
*
Haplotype A haplotype ( haploid genotype) is a group of alleles in an organism that are inherited together from a single parent. Many organisms contain genetic material ( DNA) which is inherited from two parents. Normally these organisms have their DNA o ...
* Human mitochondrial DNA haplogroup * Human mitochondrial genetics *
Human Y-chromosome DNA haplogroup In human genetics, a human Y-chromosome DNA haplogroup is a haplogroup defined by mutations in the non- recombining portions of DNA from the male-specific Y chromosome (called Y-DNA). Many people within a haplogroup share similar numbers of ...
* Most recent common ancestor *
Non-paternity event In genetics, a non-paternity event (also known as misattributed paternity, not parent expected, or NPE) is the situation in which someone who is presumed to be an individual's father is not in fact the biological father. This presumption of NPE is ...
*
List of Y-chromosome haplogroups in populations of the world The following articles are lists of human Y-chromosome DNA haplogroups found in populations around the world. *Y-DNA haplogroups by ethnic group * Y-DNA haplogroups in populations of Europe *Y-DNA haplogroups in populations of the Near East *Y- ...
*
Y-STR A Y-STR is a short tandem repeat (STR) on the Y-chromosome. Y-STRs are often used in forensics, paternity, and genealogical DNA testing. Y-STRs are taken specifically from the male Y chromosome. These Y-STRs provide a weaker analysis than autoso ...
(Y-chromosome short tandem repeat)


References


Further reading


Books

* ''Early book on adoptions, paternity and other relationship testing. Carmichael is a founder of GeneTree.'' * * * * * * ''Survey of major populations.'' * * ''Out of date but still worth reading.'' * ''Early guide for do-it-yourself genealogists.'' * * ''Guide to the subject of family medical history and genetic diseases.'' * ''Names the founders of Europe’s major female haplogroups
Helena Helena may refer to: People *Helena (given name), a given name (including a list of people and characters with the name) *Katri Helena (born 1945), Finnish singer *Helena, mother of Constantine I Places Greece * Helena (island) Guyana * H ...
,
Jasmine Jasmine ( taxonomic name: ''Jasminum''; , ) is a genus of shrubs and vines in the olive family (Oleaceae). It contains around 200 species native to tropical and warm temperate regions of Eurasia, Africa, and Oceania. Jasmines are widely culti ...
, Katrine, Tara,
Velda Velda is a name given to the hypothetical ancestress of the Cantabrian people and Haplogroup V (mtDNA). She was coined in the book ''The Seven Daughters of Eve'' by Bryan Sykes. Theoretically, based on DNA studies, she lived in the region of th ...
, Xenia, and Ursula.'' * * * * "Highly recommended book for beginners by various professional genetic genealogists and advanced amateur genealogists, and on genetic genealogy Facebook groups".


Documentaries


Journals

* * * * * * * * * * * * * * * * * * * * * *


External links


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