Y chromosome DNA tests

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A Y chromosome DNA test (Y-DNA test) is a genealogical DNA test which is used to explore a man's patrilineal or direct father's-line ancestry. The Y chromosome, like the patrilineal surname, passes down unchanged from father to son. A man's test results are compared to another man's results to determine the time frame in which the two individuals shared a most recent common ancestor or MRCA. If their test results are a perfect or nearly perfect match, they are related within a genealogical time frame. Each person can then look at the other's father-line information, typically the names of each patrilineal ancestor and his spouse, together with the dates and places of their marriage and of both spouses' births and deaths. The two matched persons may find a common ancestor or MRCA, as well as whatever information the other already has about their joint patriline or father's line prior to the MRCA. Y-DNA tests are typically co-ordinated in a surname DNA project. And each receives the other's contact information if the other chose to allow this.

Women who wish to determine their direct paternal DNA ancestry can ask their father, brother, paternal uncle, paternal grandfather, or a cousin who shares the same surname lineage (the same Y-DNA) to take a test for them.

Contents

What gets tested

Y-DNA testing involves looking at Y-STR segments of DNA on the Y chromosome. The STR segments which are examined are referred to as genetic markers and occur in what is considered non-coding DNA or "junk" DNA.

STR markers

A chromosome contains sequences of repeating nucleotides known as short tandem repeats (STRs). The number of repetitions varies from one person to another and a particular number of repetitions is known as an allele of the marker. An STR on the Y chromosome is designated by a DYS number (DNA Y-chromosome Segment number). The example below shows the allele of Rumpelstiltskin's DYS393 marker is 12, also called the marker's "value". The value 12 means the DYS393 sequence of nucleotides is repeated 12 times—with a DNA sequence of (AGAT)12.

SNP markers

A single-nucleotide polymorphism (SNP) is a change to a single nucleotide in a DNA sequence. The relative mutation rate for an SNP is extremely low. This makes them ideal for marking the history of the human genetic tree. SNPs are named with a letter code and a number. The letter indicates the lab or research team that discovered the SNP. The number indicates the order in which it was discovered. For example M173 is the 173rd SNP documented by the Human Population Genetics Laboratory at Stanford University, which uses the letter M.

Understanding test results

Y-DNA tests generally examine 10-67 STR markers on the Y chromosome, but over 100 markers are available. STR test results provide the personal haplotype. SNP results indicate the haplogroup.

Haplotype

A Y-DNA haplotype is the numbered results of a genealogical Y-DNA test. Each allele value has a distinctive frequency within a population. For example, at DYS455, the results will show 8, 9, 10, 11 or 12 repeats, with 11 being most common. For high marker tests the allele frequencies provide a signature for a surname lineage.

Kit Surname Haplo 3
9
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3
9
0

 
1
9


 
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9
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3
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11111 Rumpelstiltskin Q 12 23 13 10 16 17 12 12 13 14 14 31 18 8 9 11 11 27 13 19 28 14 14 15 15

The test results are then compared to another project member's results to determine the time frame in which the two people shared a most recent common ancestor (MRCA). If the two tests match perfectly on 37 markers, there is a 50% probability that the MRCA was fewer than 2 to 3 generations ago, a 90% probability that the MRCA was fewer than 5 generations ago, and a 95% probability that the MRCA was fewer than 7 generations ago.

Kit Surname Haplo 3
9
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11111 Rumpelstiltskin Q 12 23 13 10 16 17 12 12 13 14 14 31 18 8 9 11 11 27 13 19 28 14 14 15 15
11178 Rumpelstiltskin Q 12 23 13 10 16 17 12 12 13 14 14 31 18 8 9 11 11 27 13 19 28 14 14 15 15

STRs results may also indicate a probable haplogroup, though this can only be confirmed by specifically testing for that haplogroup's single-nucleotide polymorphisms (SNPs).

Articles

FTDNA resources

Y-DNA resources

Examples

Specific examples of the application of Y-DNA testing using the case of Thomas Jefferson and results from the the Spearin Surname Project can be seen in this video presentation by Maurice Gleeson:

See also

Licence

This article is licensed under the GNU Free Documentation Licence. It incorporates material from the Wikipedia article "Genealogical DNA test".