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Reading and Comparing DNA Test Results

Y-DNA Tests

The scientific advisory board at Family Tree DNA developed our panels of markers based on each marker' volatility. A marker that almost never mutates would yield no information of relevance. Using a panel of such slow markers would lead to many matches. It would therefore give the false impression of two individuals being related, when in fact they are not. On the other hand, we don't want a marker that is too fast changing, since it will create too much confusion when trying to identify family branches.

(+) Y-STR

When comparing y-Chromosome DNA test results to others, the surname is a important element. Depending on your ancestral country, hereditary surnames were adopted at different times. In China, hereditary family names date back to before 2000 BCE. For England, most people had adopted hereditary surnames by 1400. In Scotland and Wales hereditary names were not adopted until the 1700s. In Sweden, they were not formally adopted until 1901. The use of surnames combined with Y DNA testing sets a limit in the past for considering relationships. When a Y DNA result matches and the surname or variant matches, the two people are related since the adoption of surnames. The likely country of origin is critical then for considering how much impact a matching surname should have on your interpretation of results.

Although surnames were adopted only recently in Sweden they have extensive genealogical records. The availability of collaborative records is also an important factor to consider when evaluating test results. When utilizing Y DNA testing with genealogical research, a paper trail may define the relationship between individuals. By testing two individuals in a documented family tree, you can confirm the paper research. When the two individuals Y DNA results match or are a close match the paper trail is confirmed.

There are many applications for Y-DNA testing to genealogy research. These range from the example above of confirming the paper research, to more advanced applications such as determining the number of points of origin for a surname, and finding the ancestral homeland.

When you join a y-chromosome lineage or geographic project your results will be compared to other project members.

When comparing results between individuals with the same surname, there can be a variety of situations. In the chart above, the first two individuals are what is called a 12/12 match. They match each other exactly on the Y-DNA 12 test. The third twelve marker result on the chart does not match the other two results, and therefore it is inconclusive in terms of establishing whether there is a relationship or not.

The scientists provide estimates of the time frame for being related. These estimates depend on the number of markers tested. The more markers tested, and the higher the number of markers that match, the higher the likely hood that the common ancestor occurred more recently.

Examples of Y-DNA 37 test results are also shown above. There is one result which matches on twelve Markers to the other thirty-seven marker results, and then the balance of the result does not match closely. This result illustrates the value of testing more markers. The time frame for relatedness for twelve markers is much longer than the time frame for thirty-seven and sixty-seven markers.

The 37/37 marker matches and the 36/37 marker matches with the same suspected lineage are the type of results one would expect to receive when testing closely related people with Y-DNA testing. These results are then interpreted in relationship to the genealogical research and in relationship to the results of others with the same surname. The larger the set of results, the easier interpretation becomes.

mtDNA Tests

In most societies, the amount of historic documentation is limited. This makes tracing a female line challenging. We often have our paper trail change to the brickwall much sooner than for male lines. Testing mitochondrial DNA can help replace lost records and show us genetic connections where there are not records. When mitochondrial DNA results do not match, they conclusively disprove a suspected relationship.

Your mtDNA results will be presented in the form of a table with differences from the revised Cambridge Reference Sequence, CRS. It will look like this:

Table 1

When you join a lineage or geographic project your results will be compared to others in the project.

CRS Table

In order to make it easier to understand what Table A refers to we have highlighted in red one of the mutations (16264T) at the CRS Table. It represents one of the differences between this mtDNA sequence and the Cambridge Reference Sequence (CRS). A red-letter T in position 16264 shows that you have a T in place of the G listed for that position in the Cambridge sequence. In some cases you will see insertions or deletions in your mtDNA sequence. If you have an insertion after base pair 255, for example, the insertion will be listed as 255.1C. In this case a single base pair insertion has been found in your mtDNA string, noted by the .1 and the protein is Cytosine, denoted by the C. If you have a 2 base pair insertion the results will look like this: 255.1C 255.2T. It is also possible that you have a deletion, where a base pair that was not copied and you just don't have a base pair at that particular place. A deletion looks like this: 224 - . The dash signifies that the location, 224 isn't in your mtDNA sequence and is represented by a minus sign at the site where the protein should have been found.

Your analysis highlights these mutations and may be compared to other individual’s mutations. Our database will be helpful in finding other individuals with exactly the same mtDNA. This exact duplication of the mtDNA means two individuals shared a common female ancestor. Since the mutation rate of the mtDNA is much slower than the Y-DNA, the probablilities associated with the time to a Most Recent Common Ancestor in a case of perfect mach will point to a common ancestor living farther back than in the case of the Y-DNA. Research over the last decade has suggested several maternal lines ultimately all originating from the first woman “Eve” approximately 140,000 years ago in Africa.