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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.

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. 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 tests

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) testing

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 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). 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 results

A Y-DNA test ranges from 10 to 67 markers on the Y chromosome. It is important to check the number of markers that will be tested before choosing a test. For example, the Genographic Project only looks at 12 markers, while most laboratories and surname projects recommend testing at least 25. The more markers that are tested, the more discriminating and powerful the results will be. A 12 marker test is usually not discriminating enough to provide conclusive results for a common surname. Test results tell how many repeats a given subject has at a particular marker; the variations of repeats are known as alleles. For example, at DYS455, the results will show 8, 9, 10, 11 or 12 repeats[Ybase statistics]. 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

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.
Enlarge
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 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

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.

Human Y-chromosome DNA haplogroups
|
A |
B |
C | F
D E G H I J K
L M | P
N O Q R

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
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:

Ethnic tests

Biogeographical ancestry

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 describes these four ethnic groups as follows:

A personal genetic analysis can be performed by some companies that identify 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 assigned a likelihood of membership in thirteen major geographical regions:

Native American ancestry

A mitochondrial haplogroup determination test based on mutations in Hypervariable Region I + II may establish tribal affiliation (though not all tribes consider it appropriate to consider genetics in assessing affiliation). Autosomal testing, Y-DNA, and mtDNA testing can also be conducted to determin Native American ancestry.

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 putatively determined by Y-DNA.

European testing

European maternal clan testing
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 testing
SNP testing may enable mostly-European individuals to determine to which Sub-European population they belong:

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." There is, in fact, no genetic test that can determine religion, but this can determine relatedness within the constructs of the Hindu gotra, or clan system, an ethnic grouping, rather than a religious one.

Melungeon testing

Though some companies provide additional Melungeon research materials with Y-DNA and mtDNA tests, any test will allow comparisons with the results of current and past Melungeon DNA studies.

Benefits

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.

Medical information

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. A more specific test is used for medical purposes, which focuses on a particular gene or set of genes.

References

See also

External links

Test comparisons

Haplogroup prediction

 

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.

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