Genealogical DNA test

From Freepedia

A genealogical DNA test involves examining the nucleotides at specific locations on a person's DNA. The test results have no medical value and cannot determine genetic diseases or disorders; they are only used for genetic genealogy.

Contents

Procedure

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. Certain laboratories store DNA samples for ease of future testing whereas others destroy them, guaranteeing that a sample is not available for further analysis.

Types of tests

Genealogical DNA tests allow one to identify their recent and far distant ethnic and geographic origins. Most commonly, one uses Y chromosome (Y-DNA) testing and mitochondrial DNA (mtDNA) testing. Y-DNA & mtDNA tests are by far the most common and often people refer to them as the only genealogical DNA tests. However, additional tests are available for distant and recent ethnic origins.

Y chromosome (Y-DNA) testing

A man's paternal ancestry can be traced using the DNA on his Y chromosome (Y-DNA). 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 tested

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).

Understanding test results

A Y-DNA test will look at 10-43 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) testing

Image:Map-of-human-migrations.jpg

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 believed to be passed down by the mother unchanged, though some controversy exists over this theory. All test results are compared to the mtDNA of a European woman, 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 haplogroup

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 testing

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.

Y-DNA and mtDNA SNP tests can be ordered from Family Tree DNA. Y-DNA SNP tests (Y-SNP tests) can be ordered from DNA Heritage.

Family Tree DNA also offers a sub-clade test for mtDNA Haplogroup H. This will determine subdivisions within Haplogroup H.

Haplogroup prediction

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
9
  		4
5
5
  		4
5
4
  		4
4
7
  		4
3
7
  		4
4
8
  		4
4
9
  		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 11 11 11 23 16 21 31 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 tests

Biogeographical ancestry

Autosomal DNA testing is used 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.

As of 2005, there are 3 main DNA ethnicity testing companies, which are as follows, along with the price of their test:

Native American ancestry

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. It also offers autosomal testing through Relative Genetics and DNAPrint. Sample Native American DNA Ancestry Report.

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

[1] 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 ancestry

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 ancestry

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 testing

British tribe testing

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

European maternal clan testing

For people with European maternal ancestry, Oxford Ancestors offers an mtDNA test to determine which of eight European maternal "clans" your direct-line maternal ancestor belonged to.

Sub-European population testing

AncestryByDNA offers a SNP test for 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 testing

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."

Melungeon 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. See also the Melungeon Surname DNA Project.

Benefits

Main article: Genetic genealogy

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.

Drawbacks

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.

See also

External links

Test comparisons

Haplogroup prediction

Testing companies

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