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Genetic genealogy is the application of genetics to traditional genealogy. Genetic genealogy involves the use of genealogical DNA testing to determine the level of genetic relationship between individuals.
The investigation of surnames in genetics can be said to go back to George Darwin, a son of Charles 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 between 2.25% and 4.5% for cousin-marriage in the population of Great Britain, with the upper classes being on the high end and the general rural population on the low end. (His parents, Charles Darwin and Emma Wedgwood, were first cousins.)
Bryan Sykes, a molecular biologist at Oxford University tested the new methodology in general surname research . His study of the Sykes surname obtained valid results by looking at only four markers on the male chromosome. It pointed the way to genetics becoming a valuable assistant in the service of genealogy and history. The first company to provide direct-to-consumer genetic DNA testing was GeneTree, founded in 1997 by a graduate of Wayne State University’s Center for Molecular Medicine and Genetics, Terrence Carmichael, who earned a master’s degree in molecular biology and genetics in 1995. Genetree did not offer multi-generational genealogy tests initially. Carmichael declared, “Over 95 percent of our first-year business was in paternity testing.” In fall 2001, GeneTree sold its assets to Salt Lake City-based Sorenson Molecular Genealogy Foundation which originated in 1999.
In 2001, Sykes went on to write the popular book The Seven Daughters of Eve, which described the seven major haplogroups of European ancestors. In the wake of the book's success, and with the growing availability and affordability of genealogical DNA testing, genetic genealogy as a field began growing 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, had risen dramatically.
The Genographic Project is 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 are primarily anthropological, not genealogical. The project says 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.
More state-of-the-art commercial laboratories now recommend testing at least 25 markers, since the more markers tested, the more discriminating and powerful the results will be. A 12-marker STR test is usually not discriminating enough to provide conclusive results for a common surname. Genetic laboratories such as Genebase and Family Tree DNA give the option of testing up to 111 Y-DNA Markers.
Annual sales of genetic genealogical tests for all companies, including the laboratories that support them, are estimated to be in the area of $60 million (2006).
Paternal and maternal lineages via DNA testing
The two most common types of genetic genealogy tests are Y-DNA (paternal line) and mtDNA (maternal line) genealogical DNA tests. Note that Y chromosome and Y-DNA are used interchangeably in this article.
These tests involve the comparison of certain sequences of the DNA of pairs of individuals in order to estimate the probability that they share a common ancestor in a genealogical time frame and, through the use of a Bayesian model published by Bruce Walsh, to estimate the number of generations separating the two individuals from their most recent common ancestor or "mrca".
Y-DNA testing involves short tandem repeat (STR) and, sometimes, single nucleotide polymorphism (SNP) testing of the Y-chromosome. The Y-chromosome is present only in males and reveals information strictly on the paternal line. These tests can provide insight into the recent (via STRs) and ancient (via SNPs) genetic ancestry. A Y-chromosome STR test will reveal a haplotype, which should be similar among all male descendants of a male ancestor. SNP tests are used to assign people to a paternal haplogroup, which defines a much larger genetic population.
mtDNA testing involves sequencing or testing the HVR-1 region, HVR-2 region or both. An mtDNA test may also include the additional SNPs needed to assign people to a maternal haplogroup—or even include the complete mtDNA.
Either Y-DNA or mtDNA test results can be compared to the results of others via private or public DNA databases.
Biogeographical and ethnic origins
Genetic genealogy has revealed astonishing links between peoples. For instance, it has shown that the ancient Phoenician people were ancestors of much of the present-day population of the island of Malta. Preliminary results from a study by Pierre Zalloua of the American University of Beirut and Spencer Wells, supported by a grant from National Geographic's Committee for Research and Exploration, were published in the October 2004 issue of National Geographic. One of the conclusions is that "more than half of the Y chromosome lineages that we see in today's Maltese population could have come in with the Phoenicians."
Genealogical DNA testing methods are also being used on a longer time scale to trace human migratory patterns. For example, they have been used to determine when the first humans came to North America and what path they followed.
For several years, a number of researchers and laboratories from around the world have been sampling indigenous populations from around the globe in an effort to map historical human migration patterns. Recently, several projects have been created that are aimed at bringing this science to the public. One example, mentioned in History above, is the National Geographic Society's Genographic Project, which aims to map historical human migration patterns by collecting and analyzing DNA samples from over 100,000 people across five continents. Another example is the DNA Clans Genetic Ancestry Analysis, which measures a person's precise genetic connections to indigenous ethnic groups from around the world.
Typical customers and interest groups
Male DNA testing customers most often start with a Y chromosome test to determine their father's paternal ancestry. Females generally begin with a mitochondrial test to trace their ancient maternal lineage, which males often have tested for the same purpose.
A common consumer goal in purchasing DNA testing services is to acquire quantified, scientific linkage to a specific ancestral group. A compelling example of this motive is found in the expressed desires of some consumers to be proven to have Viking paternal ancestry. In keeping with this marketplace demand, one British DNA testing service, Oxford Ancestors, offers a Y chromosome test purporting to assess whether given males are of "Viking stock." Those whose DNA falls into the designated haplogroup are issued Viking Descendant certificates by the testing service. The same DNA testing company participated in producing a televised documentary, "The Blood of the Vikings," in conjunction with the BBC, which showed how DNA testing could reveal Viking ancestry.
The RootsWeb Genealogy-DNA Internet discussion group has a membership of 750 subscribers from around the world. Some subscribers have had various DNA tests performed and are seeking advice and guidance in interpreting their results. The list also includes administrators of DNA projects that examine surnames, geographic regions, or ethnic groups. The sophistication of subscribers ranges from expert to novice. In some cases, subscribers have been credited with making useful and novel contributions to knowledge in the field of genetic genealogy.
Paternal and maternal DNA lineages
Mitochondria are organelles that lie in the cytoplasm of eukaryotic cells, such as those of humans. Their primary purpose is to provide energy to the cell. Mitochondria are thought to be the vestigial remains of symbiotic bacteria that were once free living. One indication that mitochondria were once free living is that they contain their own circular DNA genome, mitochondrial DNA (mtDNA). Mitochondrial DNA is independent of autosomal DNA contained in chromosomes in the nucleus of the cell. Individuals inherit their cytoplasm and the organelles it contains exclusively from their mothers. The mitochondrial of the sperm are destroyed when the ovum (egg cell) is fertilized.
When a mutation arises in mtDNA molecule, the mutation is therefore passed in a direct female line of descent. These rare mutations are derived from copying mistakes—when the DNA is copied it is possible that a single mistake occurs in the DNA sequence, an outcome which is called a single nucleotide polymorphism (SNP).
Human Y chromosomes are male-specific sex chromosomes; nearly all humans that possess a Y chromosome will be morphologically male. Y chromosomes are therefore passed from father to son; although Y chromosomes are situated in the cell nucleus, they only recombine with the X chromosome at the ends of the Y chromosome; the vast majority of the Y chromosome (95%) does not recombine. When mutations (SNPs, and STR copying mistakes) arise in the Y chromosome, they are passed down directly from father to son in a direct male line of descent. The Y-DNA and mtDNA therefore share a certain feature: they both pass down unchanged except for mutations.
The other chromosomes, autosomes and X chromosomes in women, share their genetic material (called crossing over leading to recombination) during meiosis (a special type of cell division that occurs for the purposes of sexual reproduction). Effectively this means that the genetic material from these chromosomes gets mixed up in every generation, and so any new mutations are passed down randomly from parents to offspring.
The special feature that both Y-DNA and mtDNA share, above, preserves a "written" record of their mutations because neither DNA gets mixed up or randomized—mutations remain fixed in place on both types of DNA. Furthermore the historical sequence of these mutations can also be inferred. For example, if a set of ten Y chromosomes (derived from ten different men) contains a mutation, A, but only five of these chromosomes contain a second mutation, B, it must be the case that mutation B occurred after mutation A.
Furthermore all ten men who carry the chromosome with mutation A are the direct male line descendants of the same man who was the first to carry this mutation. The first man to carry mutation B was also a direct male line descendant of this man, but is also the direct male line ancestor of all men carrying mutation B. Series of mutations such as this form molecular lineages. Furthermore each SNP mutation may define a set of specific Y chromosomes called a haplogroup.
All men carrying SNP mutation A form a single haplogroup, and all men carrying mutation B are part of this haplogroup, but mutation B (if a SNP) may also define a more recent haplogroup (which is a subgroup or subclade) of its own which men carrying only mutation A do not belong to. Both mtDNA and Y chromosomes or Y-DNA are grouped into lineages and haplogroups; these are often presented as tree-like diagrams.
Genetic distance among relatives
Where the genogram or family tree of individuals is known, it can be used to determine the genetic identity between individuals. It is often described as percentage of genetic identity, referring to the fraction of genome inherited from common ancestors, and not actual genomic identity, which is always approximately 99.9% identical from one human to another.
One method of calculating this genetic similarity is to do an inbreeding calculation by the path or tabular method and then multiply by 2, because any progeny would have a 1 in 2 risk of actually inheriting the identical alleles from both parents. For instance, a brother/sister relation gives 25% risk for two alleles to be identical by descent.
- Allele frequency
- Family name
- Genealogical DNA test
- Genetic recombination
- Human mitochondrial DNA haplogroups
- Human Y-chromosome DNA haplogroups
- Human mitochondrial genetics
- Human genetic clustering
- Most recent common ancestor
- Short tandem repeat (STR)
- Single nucleotide polymorphism (SNP)
- Y-STR (Y-chromosome short tandem repeat)
- Y-chromosome haplogroups by populations
- Non-paternity event
- George H. Darwin, "Note on the Marriages of First Cousins", Journal of the Statistical Society of London 38:3 (Sep., 1875), pp. 344-348. DOI
- editor, "CMMG alum launches multi-million dollar genetic testing company", Alum notes, Wayne State University, School of Medicine's alumni journal, Vol. 17, num.2, Spring 2006 page 1, accessed 24 Jan 2013
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- Terrence Carmichael and Alexander Kuklin (2000). How to DNA Test Our Family Relationships. DNA Press. Early book on adoptions, paternity and other relationship testing. Carmichael is a founder of GeneTree.
- L. Cavalli-Sforza et al. (1994). The History and Geography of Human Genes. Princeton: Princeton University Press.
- Luigi-Luca and Francesco Cavalli-Sforza (1998). The Great Human Diasporas, translated from the Italian by Sarah Thorne. Reading, Mass. : Perseus Books.
- Colleen Fitzpatrick and Andrew Yeiser (2005). DNA and Genealogy. Rice Book Press.
- Clive Gamble (1993). Timewalkers: The Prehistory of Global Colonization. Stroud: Sutton.
- M. Jobling (2003). Human Evolutionary Genetics.
- Steve Olson (2002). Mapping Human History. Boston: Houghton Mifflin Company. Survey of major populations.
- Stephen Oppenheimer (2003). The Real Eve. Modern Man’s Journey out of Africa. Carroll & Graf.
- PBS (2003). The Journey of Man DVD. Broadcast aired in January 2003, Spencer Wells, host.
- Donald Panther-Yates and Elizabeth Caldwell Hirschman (2006). “DNA Haplotyping and Diversity: An Anthropogenealogical Method for Researching Lineages and Family Ethnicity,” International Journal of the Humanities 2:2043-55. Guide to finding matches in world databanks and interpreting genetic information in terms of history and recent emigration studies.
- Chris Pomery (2004) DNA and Family History: How Genetic Testing Can Advance Your Genealogical Research. London: National Archives. Early guide for do-it-yourself genealogists. Now updated (2007) as Family History in the Genes: Trace Your DNA and Grow Your Family Tree.
- Alan Savin (2003). DNA for Family Historians. Maidenhead: Genetic Genealogy Guides.
- Thomas H. Shawker (2004). Unlocking Your Genetic History: A Step-by-Step Guide to Discovering Your Family's Medical and Genetic Heritage (National Genealogical Society Guide, 6). Guide to the difficult subject of family medical history and genetic diseases.
- Megan Smolenyak and Ann Turner (2004). Trace Your Roots with DNA: Using Genetic Tests to Explore Your Family Tree. Rodale Books, ISBN 978-1-59486-006-5. Recent tool for amateur genealogists by seminar speaker and DNA listserv moderator.
- Bryan Sykes (2001) The Seven Daughters of Eve. The Science that Reveals Our Genetic Ancestry. New York, Norton. Names the founders of Europe’s major female haplogroups Helena, Jasmine, Katrine, Tara, Velda, Xenia, and Ursula.
- Linda Tagliaferro (1999). The Complete Idiot’s Guide to Decoding Your Genes. Alpha Books.
- Spencer Wells (2004). The Journey of Man. New York: Random House.
- National Geographic's interactive Atlas of the Human Journey (Flash required)
- Y-DNA Ethnographic and Genographic Atlas and Open-Source Data Compilation
- MSNBC — Genetic Genealogy Front Page