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Genealogical DNA test

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A genealogical DNA test involves examining the nucleotides at specific locations on a person's DNA. The tests results are meant to have no informative medical value and do not determine specific genetic diseases or disorders (see possible exceptions in Medical information below); they are intended only for use in genetic genealogy.

ProcedureEdit

The general procedure for taking a genealogical DNA test involves taking a painless cheek-scraping at home and mailing the sample to a genetic genealogy laboratory for testing. Some laboratories use mouth wash or chewing gum instead of cheek swabs. Most of the laboratories offer to store DNA samples for ease of future testing. All laboratories will destroy the DNA sample upon request by the customer, guaranteeing that a sample is not available for further analysis.

Types of testsEdit

Genealogical DNA tests allow one to compare their DNA with that of others. They are also used to identify possible recent and far distant ethnic and geographic origins. The most popular such tests are Y chromosome (Y-DNA) testing and mitochondrial DNA (mtDNA) testing. Other, less well validated tests attempt to determine distant and recent ethnic origins.

Y chromosome (Y-DNA) testingEdit

A man's paternal ancestry can be traced using the DNA on his Y chromosome (Y-DNA). This is particularly useful because the Y chromosome, like many European surnames, passes from father to son, and can be used to help study surnames. Women who wish to determine their paternal ancestry can ask their father, brother, paternal uncle, paternal grandfather, or a cousin who shares the same paternal lineage to take a test for them (i.e. any male family member who has the same surname as her father).

What gets testedEdit

Y-DNA testing involves looking at segments of DNA on the Y chromosome (found only in males) where sequences of nucleotides repeat, known as short tandem repeats (STRs). These segments are considered "junk" DNA. The segments which are examined are referred to as genetic markers and are designated by a DYS number (DNA Y-chromosome Segment number). These STRs may also indicate a likely haplogroup for the Y chromosome, though this can only be confirmed by specifically testing for that haplogroups' single nucleotide polymorphisms (SNPs).

Understanding test resultsEdit

A Y-DNA test will look at between 10 and 43 markers on the Y chromosome. The results will tell how many repeats the test subject had at any given marker; the variations of repeats are known as alleles. For example, at DYS455, the results will show 8, 9, 10, 11 or 12 repeats (source). The test results are then compared to another person's results to determine the time frame in which the two people shared a most recent common ancestor (MRCA). If the two tests match on 37 markers, there is a 50% probability that the MRCA was less than 5 generations ago and a 90% probability that the MRCA was less than 17 generations ago.

Mitochondrial DNA (mtDNA) testingEdit

Map-of-human-migrations

Map of human migration, according to mitochondrial DNA. The numbers represent thousands of years before present time. The blue line represents the area covered in ice or tundra during the last great ice age. The North Pole is at the center. Africa, harboring the start of the migration, is at the top left and South America is at the far right.

A person's maternal ancestry can be traced using his or her mitochondrial DNA (mtDNA). The DNA in the mitochondria (an organelle inside most cells) is generally passed down by the mother unchanged, though some exceptions have been shown. All test results are compared to the mtDNA of a European woman in haplogroup H, which is known as the Cambridge Reference Sequence (CRS). Any "mutations" or "transitions" that are found are simply differences from the CRS. The test results are compared to another person's results to determine the time frame in which the two people shared a most recent common ancestor (MRCA).

Haplotype and haplogroupEdit

A Y-DNA haplotype is simply the numbered results of a genealogical Y-DNA test. For example, as of July 2005, the Mumma DNA Surname Project had Y-DNA tested 65 men, and had correlated the results to conclude a modal haplotype for the Mumma surname. This is the most likely haplotype of the oldest Mumma ancestor.

Haplogroups are large groups of haplotypes that can be used to define genetic populations and are often geographically oriented.

Haplogroup SNP testingEdit

Human Y-chromosome haplogroups are not defined by haplotype but by single nucleotide polymorphisms (SNPs), which are locations on the DNA where one nucleotide has "mutated" or "switched" to a different nucleotide. A variation must occur in at least 1% of the population to be considered a SNP.

A person's haplogroup can often be inferred from their haplotype, but can only be proven with a Y-chromosome SNP tests (Y-SNP test). In addition, some companies offer sub-clade tests, such as for Haplogroup H.

Haplogroup predictionEdit

A Y-DNA or mtDNA test will usually result in a haplogroup prediction. Because of the strong correlation between haplogroups and haplotypes, it is sometimes possible to determine the haplogroup without a SNP test.

For example, Haplogroup G has a known modal haplotype:

DYS markers 3
8
5
a
3
8
5
b
3
8
8
 
3
8
9
i
3
8
9
ii
3
9
0
 
3
9
1
 
3
9
2
 
3
9
3
 
3
9
4
 
4
2
6
 
4
3
7
 
4
3
9
 
4
4
7
 
4
4
8
 
4
4
9
 
4
5
4
 
4
5
5
 
4
5
8
 
4
5
9
a
4
5
9
b
4
6
4
a
4
6
4
b
4
6
4
c
4
6
4
d
Haplogroup G: Modal STR values 14 14 12 12 29 22 10 11 14 15 11 16 11 23 21 31 11 11 16 9 9 12 13 13 14

Few haplotypes will exactly match the modal values for Haplogroup G. One can consult an allele frequency table to determine the likelihood of remaining in Haplogroup G based on the variations observed.

Additional predictions include:

  • If DYS426 is 12 and DYS392 is 11, one is probably a member of haplogroup R1a1.
  • If DYS426 is 12 and DYS392 is not 11, one is probably a member of haplogroup R1b.
  • If DYS426 is 11, one is probably a member of haplogroup G,I, or J.
  • If DYS426 is 11 and DYS388 is 12, one is probably a member of haplogroup N3 or E3b

Ethnic testsEdit

Biogeographical ancestryEdit

Autosomal DNA testing purports to determine the "genetic percentage" of certain ethnicities in a person. These tests examine SNPs, which are locations on the DNA where one nucleotide has "mutated" or "switched" to a different nucleotide. These tests are designed to tell what percentage Native American, European, East Asian, and African a person is. These tests are controversial—their validity has not been independently confirmed—and the results are often disputed.

AncestryByDNA, an autosomal DNA testing company, describes these four ethnic groups as follows:

  • Native American: Populations that migrated from Asia to inhabit North, South and Central America.
  • European: European, Middle Eastern and South Asian populations from the Indian subcontinent, including India, Pakistan and Sri Lanka.
  • East Asian: Japanese, Chinese, Mongolian, Korean, Southeast Asian and Pacific Islander populations, including populations native to the Philippines.
  • African: Populations from Sub-Saharan Africa such as Nigeria and Congo region.

DNA Consulting offers AncestryByDNA 2.5 and EURO DNA and provides an evaluation that interprets some of the biases and weaknesses of these tests, such as confusion of East Asian and Native American percentages and lack of a category for Iberian DNA. AncestryByDNA 3.0 will be available in Fall 2005.

DNA Tribes offers a Geo-Genetic profile that identifies the indigenous and diaspora populations in which an individual's autosomal STR profile is most common. This test examines autosomal STRs, which are locations on a chromosome where a pattern of two or more nucleotides is repeated and the repetitions are directly adjacent to each other. The populations in which the individual's profile is most common are identified and assigned a likelihood score. The individual's profile is also compared to four continental groups (European, East and South Asian, Native American, and Sub-Saharan African), and likelihood of membership in each group is indicated.

As of 2006, there are 4 main DNA ethnicity testing companies, which are as follows, along with the price of their test:

Native American ancestryEdit

DNA Consulting offers a mitochondrial haplogroup determination test based on mutations in Hypervariable Region I + II. It is the only DNA testing company that is Native-owned and says that tribal affiliation can often be established (though not all tribes consider it appropriate to consider genetics in assessing affiliation). It also offers autosomal testing through Relative Genetics and DNAPrint. Sample Native American Report

GeneTree offers autosomal, Y-DNA, and mtDNA testing for Native American ancestry.

Trace Genetics offers mtDNA and Y-chromosome SNP typing for biogeographic ancestry testing. Trace Genetics has compiled the largest database of Native American mtDNA presently available.

African ancestryEdit

African Ancestry offers Y-DNA and mtDNA testing to determine with which present-day African country the direct-line paternal lineage or direct-line maternal lineage shares its ancestry.

Cohanim ancestryEdit

Cohanim ancestry (sharing a set of markers with the family of the Biblical figure Aaron) is determined by Y-DNA testing from Family Tree DNA.

European testingEdit

British tribe testingEdit

For people whose paternal ancestors came from the British Isles, Oxford Ancestors offers a Y-DNA test that claims to determine which British tribe the direct-line paternal ancestor belonged to.

European maternal clan testingEdit

For people with European maternal ancestry, mtDNA tests are offered to determine which of eight European maternal "clans" the direct-line maternal ancestor belonged to. This is simply an mtDNA haplotype test based on the research in the book The Seven Daughters of Eve.

Sub-European population testingEdit

AncestryByDNA offers a SNP test that it states will enable mostly-European individuals to determine to which Sub-European population they belong:

  • Northern European subgroup (NOR) - mostly Northern European or Irish
  • Southeastern European (Mediterranean) subgroup (MED) - mostly Southeastern Europeans (Greeks or Turks)
  • Middle Eastern subgroup (MIDEAS) - mostly Middle Eastern
  • South Asian subgroup (SA) - mostly South Asian from the Indian sub-continent (i.e. Indian)

Hindu testingEdit

DNA Consulting uses a 13-marker (low resolution) Y-DNA test and an HVR1 (low resoultion) mtDNA test which they say can be used to "verify genetic relatedness and historical gotra genealogies for Hindu and Buddhist engagements, marriages and business partnerships." There is, in fact, no genetic test that can determine religion.

Melungeon testingEdit

Main article: Melungeon#DNA testing

DNA Consulting uses a 13 marker (low resolution) Y-DNA test or an HVS1+2 mutational mtDNA test and "a surname report on the meaning, historical connections and any Melungeon connections for your family name..." as well as articles, references and suggestions for further reading. Any Y-DNA test will allow comparisons with the results of current and past Melungeon DNA studies.

BenefitsEdit

Genealogical DNA tests have become popular due to the ease of testing and the various additions they make to genealogical research. Genealogical DNA tests allow for an individual to determine with 99.9% certainty that they are related to another individual within a certain time frame, or with 100% certainty that they are not related to another individual within a certain time frame.

DrawbacksEdit

The main reasons people cite for not wanting to be tested is the cost or concerns over privacy issues.

In addition, Y-DNA and mtDNA testing each only trace a single lineage (one's father's father's father's etc. lineage or one's mother's mother's mother's etc. lineage). At 10 generations back, an individual has 1024 ancestors (excluding intermarriages) and a Y-DNA or mtDNA test is only studying one of those 1024 ancestors.

Medical informationEdit

Though genealogical DNA tests results generally have no informative medical value and do not determine genetic diseases or disorders, there has been a correlation established between a lack of DYS464 markers and infertility, and a correlation between mtDNA haplogroup H and protection from sepsis.

See alsoEdit

External linksEdit

Test comparisonsEdit

Haplogroup predictionEdit

Testing companiesEdit

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