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Genetic genealogy: practical applications

Practical applications of genetic genealogy are explored.
In this lecture, we will look in a little more detail, at the practical use of test results from Autosomal DNA tests and Y-DNA tests. And briefly explain Mitochondrial testing. Perhaps the first thing you will notice when you receive results from an Autosomal test, is that you have a very large number of matches. Probably more than 2000. You may begin to question whether these are really all relatives, and wonder how you can use your results to answer your genealogical questions. The answer to the first question is that probably the vast majority of these individuals are related to you, but in many cases, fairly distantly.
The testing companies use a number of criteria to filter out matches which are not true genealogical matches, which ensures, with a fair degree of confidence, that the matches displayed are genuine relatives. Each match is given a predicted relationship, such as second to third cousin, second to fourth cousin, fifth to remote cousin. User experiences are showing that for more distant relationships, these predictions tend to overestimate the closeness of the relationship. In other words, a prediction of a second to fourth cousin is more likely, in reality, to be a third to fifth cousin. Those taking Autosomal DNA tests may have different questions they wish to answer.
But probably, the most common aims are to discover new relatives and to trace family origins further back in time. The second aim can become more of a possibility, if you can make contact with unknown relatives, who may have documentary evidence, or clues, to elderly or geographical origins, both of which could assist your research. So let’s consider how you can go about identifying new relatives from the very large number of matches you are faced with. You would be likely to have great difficulty in proving links with those predicted as third to fifth cousins. So focus in on any individuals you don’t already know, who are predicted as first to second, second to third, or second to fourth cousins.
Taking my own results as an example, this leaves me with 30 matches to investigate. There is an option to add a list of ancestral surnames you are interested in, to a test result, along with a family tree. So the most obvious approach is to look at any ancestral surnames your matches have listed. If these are the same as any of your own ancestral lines, it would be worth emailing the individual who is tested to compare research, and see whether documentary evidence can prove a genealogical link. This is just a very basic initial strategy. To get more out of your results, you can move on to getting more of your known relatives tested, beginning, if possible, with parents.
If both your parents have been tested, it is possible to phase your results, which means, identifying which segments of DNA you have inherited from which parent. By testing other relatives, you may be able to attempt chromosome mapping. That is trying to work out which segments of DNA have come from which ancestors. One particularly useful tool worth knowing about is GEDmatch.
This makes it possible to compare results with those who have not tested with the same company as yourself, and find further matches, perhaps closer than those you already have. GEDmatch allows the uploading of 80 DNA results from three of the major testing companies and also offers some additional features to analyse your data. Success in finding more matches depends on who else has upload their data to GEDmatch, but the site does merit investigation. An example of how Autosomal testing can be used, is the case of Alexander Izatt Jones. It was only late in his life that Alexander discovered that the Mr.
Jones whom he thought of as his father, was not his biological father, and he was keen to find out who his biological father was. Through some initial Y-DNA testing, he had discovered that he was genetically a Stewart, but the first Autosomal test he took did not provide any matches close enough to help answer the question of his paternity. However, testing with another company revealed a close match with Barbara, coloured blue on the chart, whose paternal grandmother was a Stewart. When Barbara’s father tested, coloured green on the chart, he matched closely enough to be a first cousin of Alexander Izatt Jones. Research now focused on Barbara’s Great Uncle, Willy Stewart, coloured purple.
One of Willie’s daughters, Grace, coloured red, was located and agreed to test. Her test results revealed enough matching DNA to confirm that Grace was a half-sister of Alexander. Alexander’s biological father had been identified at last as Willy Stewart. Let’s now turn our attention to Y-DNA tests. These are limited by the fact that they can only be taken by males, and only refer to an unbroken line of male ancestors. On the other hand, they have the advantage that they can provide information about this single ancestral line, going back many generations.
As you saw in the example given in the short video, the Y chromosome was passed down the male line from John Senior, to his three great grandsons, John, David, and Hugh. Although the Y chromosome does occasionally mutate, this only results in small changes. So in our example, the great grandsons will carry a Y chromosome very similar to their great grandfather, and for that matter, to their direct male line ancestor several hundred of years ago. The most commonly used type of Y-DNA test is the STR test, which aims to find similarities between results.
Since closely matching results indicate descent from a common male line ancestor, STRs, or short tandem repeats, are repeated patterns of chemical bases, which can be measured in the Y chromosome. A motif pattern could be repeated perhaps 12 times in sequence at a specific location on the chromosome. Y-DNA STR tests used for genealogy measure the number of repeats at selected locations. The most popular tests now use 37 or 67 locations. A comparison of the 37 marker test results for John, David, and Hugh show that John and David match exactly, while Hugh has a difference of one at one of the markers.
This level of matching is what would be expected and confirms the documentary evidence that they are closely related, since they are second cousins. You should note, however, that these test results can only confirm that the relationship is a close one and they are not precise enough to show that the relationship is that of a second cousin. If test results, when compared, show major differences, this indicates that the individuals are either very distantly related or not related. Tables can be consulted, which indicate what the level of probability is that they shared a common ancestor a certain number of generations ago.
One other point to be aware of is that matching of STR results can be very useful for the period from around 1500, but before that, care is required in interpretation. For the early period, SNP tests are more important, although it should still be used along with STR results. SNPs, which is short for single nucleotide polymorphisms, are mutations which occur when a single chemical base in the DNA changes at a specific location.
In the slide, you can see that the base has changed from an A, which is carried by Males 2, 3, and 4, to a T, carried by Male 1. Once this mutation has taken place, it is usually extremely stable, unlike STRs, which are prone to further changes. Because of the stable nature of SNPs, they can be used to identify a specific branch of descendants and have become much more important to genealogists, as technological advances have enabled the discovery of many more of these. Now using advanced testing techniques, it is possible to discover SNPs which occurred hundreds of years ago, rather than thousands of years ago.
This brings us into the era of recorded history, and can introduce an element of precision into test results. Whereas previously, using STR testing, the time to the most recent common ancestor could only be calculated as a percentage probability, SNPs can and have been pinpointed as occurring in a known historical figure. One example of this is the SNP CLD51, which indicates descent from the MacDonalds of Kinlochmoidart, who are descended from John MacDonald, the fifth son of Alan McDonald, ninth of Clan Ranald, who died in 1593. In addition to Autosomal and Y-DNA tests, there is another type of test which can be taken by males or females, called a Mitochondrial test.
Mitochondrial DNA testing is the opposite of Y-DNA testing, in that while Y-DNA is passed down from father to son, Mitochondrial DNA is passed down from mother to children. Although, Mitochondrial DNA is passed from mother to sons and daughters, it can only be passed on by daughters. This chart shows how Mitochondrial DNA is inherited.
Blue indicates those carrying the Mitochondrial DNA, but only the females, indicated by the blue circles, can pass this on. Another difference, and a very important one, from the point of view of genealogists, is that there are fewer recent mutations reported in Mitochondrial DNA than with Y-DNA. This means that even an exact match between two individuals may only show that they probably shared a common female line ancestor about 400 or 500 years ago.
For this reason, Mitochondrial DNA is good for telling us which part of the world a female line ancestor lived in several thousand years ago, but not so good at telling us if we are related to an individual with a close genetic match, and if so, when the common ancestor lived. Here’s a summary of the tests I have been describing.

In this video we take a look at aspects of autosomal, mitochondrial and Y-DNA testing and explore their practical applications for genealogists.

Selected slides from the video are available in the ‘Downloads’ section below. The resources in the ‘See Also’ section below can be consulted for more information on the topic.

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Genealogy: Researching Your Family Tree

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