genetic-genealogy

Genetic genealogy – Revealing ancestry and family relations using DNA

What is genetic genealogy?

Genetic genealogy is the application of genetics to genealogy. It analyses the human genome to prove or at least estimate their ancestry, i.e. the degree of kinship between individuals. Traditional genealogical approaches are limited to pedigree, extracted from official documents, hence often end in a brick wall when tracing a person’s family tree due to lack of available information. 

Genealogy research that incorporates DNA test results could break through this genealogical brick wall and trace family history further back in time. The National Genealogical Society now even has a Genetic Genealogy committee after previously depending on historical records in testing for genealogy. The popularity of DNA tests also leads to the emergence of the International Society of Genetic Genealogy (ISOGG), a non-profit organization that promotes the use of DNA testing in genealogy research.

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Genetic inheritance

Genetic genealogy is enabled by patterns of genetic inheritance. The human genome consists of DNA, our genetic materials that are located in the cell. There are two types of DNA based on where they are specifically located within the cell: nuclear DNA and mitochondrial DNA (mtDNA). Nuclear DNAs are packed in a structure called chromosome and organized in pairs with autosomal DNA organized in 22 pairs and the sex DNA in one pair. The sex DNA consists of two types of chromosomes, the X chromosomes (X-DNA) and the Y chromosome (Y-DNA). Women have two X-DNA and men have one X-DNA and one Y-DNA.

Children inherit their DNA from both parents. While the nuclear DNA of the parents recombines to form autosomal DNA in children and X-DNA in daughters, Y-DNA and mtDNA are passed on as copies. The X-DNA is inherited from the father to the daughters and from the mother to all children (X chromosomal inheritance). The Y-DNA is inherited from the father to the sons (paternal Y-chromosomal inheritance). The mtDNA is inherited from the mother to the children (maternal mtDNA inheritance). 

Nuclear DNA and mitochondrial DNA inheritance patterns enable genetic genealogy.
Nuclear DNA and mitochondrial DNA inheritance patterns enable genetic genealogy. Source: University of California Museum of Paleontology (UCMP) and the National Center for Science Education / CC-BY SA

Both recombination and copying of DNA are likely to result in mutations (e.g. due to errors by the DNA polymerase) and other hereditary defects, the effects of which range from harmless to lethal, depending on their position in the genes. Whether the mutations will cause a defect that is observable will also depend on whether the mutated genes are present in one or both chromosome pairs. Mutations can also have positive effects and thus make a decisive contribution to the evolution and act as a source of genetic variation.

DNA from any two people is 99.5% identical; the remaining differences are called genetic variation. By comparison, chimpanzees and humans share 98.8% of DNA. The appearance of humans (phenotype) is influenced by genotype, but also by non-heritable acquired traits. 

Genetic variation is not geographically uniform on earth and can, therefore, be used to approximately determine the regions in which a person’s ancestors lived. 

Genealogical DNA family trees and networks

In genealogical DNA analysis, we want to know which haplogroups a genome belongs to. Haplogroups are groups of identical genetic profiles, usually due to common ancestors. Genealogy research uses genetic markers in the haplogroups to determine the degree of kinship. As Y-DNA and mtDNA are passed on as copies, we usually used genetic markers that could identify Y-DNA and mtDNA haplogroups.

Genetic Genealogy based on Haplogroups Y-DNA (paternal)

Apart from mtDNA, only Y-DNA enables the tracing of a clear ancestral line. Y-DNA was also researched early on to establish paternal lines. The Y-DNA haplogroups are distinguished by the letters A to R, as well as numbers and lowercase letters, using a system developed by the Y Chromosome Consortium.

The haplogroup R1a occurs particularly frequently in Europe, North-Central Asia, and India. In Europe, particularly high concentrations can be found in Poland, Russia, and Northern Europe. In India, the highest concentration was found in the caste of the Brahmins.

Genetic Genealogy based on Haplogroups mtDNA (maternal)

Since mtDNA has 100-10,000 copies per cell and has a simple structure compared to the chromosomal DNA in the cell nucleus, it was preferred for low-cost analysis. In addition, the maternal line can be reconstructed from the DNA in the mitochondria.

When old remains of Homo sapiens are found, mtDNA is often still the only source of genetic information due to the degeneration of the DNA markers in the cell nucleus.

Human geneticist Bryan Sykes claims that there are seven mitochondrial lineages for the modern European (but others estimate this number at 11 or 12). However, the number of mitochondrial ancestry for the entire world population is considerably larger. With more mtDNA tests, we may find more mitochondrial lineages in the global population. 

Geographical distribution of mtDNA haplogroups (maternal):

  • Southern Europe: J, K
  • Northern Europe: H, T, U, V, X
  • Middle East: J, N
  • Africa: L, L1, L2, L3
  • Asia: A, B, C, D, E, F, G
  • America (Native Americans): A, B, C, D, X

Genetic Genealogy based on Autosomal DNA and X-DNA (origin, relationship)

As autosomal DNA and X-DNA are recombined, their DNA sections are inherited randomly from ancestors. Thus, complex mutation analyses are necessary to draw genealogical conclusions from these types of DNA. Companies that offer DNA tests for commercial purposes test approximately 700,000 autosomal SNPs. Nevertheless, they are already available from a price of €49.

In order to be able to analyze the composition of genetic lineage in relation to geographical groups (peoples, clans), a sufficient number of test persons are required, from whom the ancestors originate from a defined known area.

Depending on the form of analysis and the choice of the decisive components, or “data clusters”, different evaluations and representations are possible. The creation of family trees, for example, is possible by showing the closeness of the relationship between different subjects or clusters. With this form of presentation, the choice of the decisive component(s) is influential; even small changes in the constellation will produce different test results.

Based on matching DNA segments, statistical conclusions about the relationship can be calculated. The segments are usually compared using SNP mutations. The longer the matching segment, the closer the relationships between individuals tested. Below a certain length, however, matching segments are more likely to occur due to chance rather than descent.

Testing for genetic genealogy

More than 30 million people have now had a genealogical DNA test done by one of the four testing companies (Ancestry, 23andme, MyHeritage, FTDNA), which, according to an estimate by Dr. Yaniv Erlich, makes about 60% of white Americans identifiable by at least one-third cousin or closer in one of the databases. Companies such as Parabon NanoLabs have taken advantage of this and are offering their services to American law enforcement agencies. 

Based on a DNA sample from the crime scene, a profile is created from 850,000 SNPs, which among other things allow predictions to be made about the appearance of the perpetrator (DNA phenotyping). In addition, this profile is compatible with GEDmatch and FTDNA, so that relatives of the offender can be searched for there. 

CeCe Moore, the lead genetic genealogist at Parabon, has been able to match 110 DNA samples to the person sought within two years. In addition to solving the predominantly “cold” criminal cases, in this way she has also helped to stop active serial rapists. In May 2019, the innocence of a man who spent more than 20 years in prison for murder could be proven in one case. At the same time, the real culprit was identified and arrested.

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