1. Introduction

Over the last few decades the use of computers have played a major role in assisting the amateur genealogist to construct and enhance their family trees. This is done through access to such information as vital records, digitised newspapers and other on-line family trees. These are only a few of the available sources. Some of this information is unreliable and often it is enhanced with oral history which may even be less accurate and then at other times will produce some real pearls of family history.

With the increase in availability and reduced costs of various forms of DNA testing, this has now become a very popular way to push through some of the "brick walls" that you may encounter when using traditional means. Using DNA testing may be considered a "scientific" method, however, before embarking on this approach it is worthwhile to have a clear idea of what you are trying to achieve and whether DNA testing is going to give you the answers you are looking for. Some types of testing (e.g., Y-DNA) will give results that are close to 100% correct, whereas others (e.g.,autosomal DNA) will give results that are based on probabilities, hence require confirmation by more traditional means.

2. Types of DNA Testing

The types of DNA tests that you can have done will depend on the testing organisation you use and what outcomes you are looking for. If your aim is to find well-known or obscure genetic medical conditions that may be passed down from generation to generation, then I suggest you seek advice from your family doctor.

2.1 Autosomal DNA (atDNA)

Most (if not all) DNA testing companies provide the ability to have your atDNA tested. atDNA refers to the 22 pairs of non-sex chromosomes found within the nucleus of every cell. A child will inherit 1 chromosome in each pair from their mother and 1 chromosome in each pair from their father i.e., a child inherits his entire DNA from his parents, approximately 50% from his mother and approximately 50% from his father. To complicate this, each chromosome undergoes "recombination" before it is passed down to the next generation. In this process chromosomes are modified so that each resulting chromosome pair can (and usually is) a combination of the parents chromosomes.

From a probability points of view you can draw some conclusions about the matching obtained between 2 people via atDNA testing.

e.g.,

self --- parent 50% of atDNA will be shared

self --- son/daughter 50%

self --- grandparent 25%

self --- great grandparent 12.5%

self--- neice/nephew 25%

self --- first cousin 12.5%

self --- 2nd cousin 3.125%

self --- 3rd cousin .781%

etc.

an example of these probability tables can found on-line at https://isogg.org/wiki/Cousin_statistics

The above show the expected levels of matching, but individual cases can vary significantly and the presentation of results can be quite overwhelming. I use Family Tree DNA (FTDNA) for my testing, and the results of my atDNA tests are used in what they call their Family Finder facility. I have some 15,000 matches and for each match there is an estimate of what the relationship might be. Of these 15,000 I have found 5 people who I know I am related to. The sledge- hammer approach to this could be to contact each of these 15,000 people and ask questions about their family. Another approach would be to look at on-line family trees, where people have provided this link.

A simpler approach is to only show matches for immediate or close relatives. In this case I have 126 names appear, but only shows 2 of my known 4 (DNA) relatives. The most useful filtering facilities I have found are either to look for a specific ancestral name (using an entered name as a filter) or use the in-built facility to match using the "common surname" feature. In this case 5 (DNA) relatives appear plus another 1,000 matches. So in the end you need to do a search of names then look at associated family trees. In setting up your individual account you are asked to also enter your ancestral surnames. These are then used by the searching facilities when used by other people.

In summary, atDNA is useful for bringing potential relatives to your attention then confirming the relationship via family tree comparisons.

Most companies who do atDNA testing will also provide an "Origins" report e.g.,

At Family Tree DNA, this is achieved by examining 24 reference populations around the world that your autosomal DNA connects to. For many people, obtaining this origin information may be all they require.

2.2 X-Chromosomal (X-DNA)

Generally, when you request autosomal testing, X-DNA testing is also carried out. This is the 23rd pair of chromosomes and is one of the 2 sex-chromosomes (the other being the Y-chromosome). Women have two X chromosomes, one inherited unchanged from their father and the other inherited from their mother. Men have just one X chromosome that they inherit from their mother (and one Y-chromosome, inherited from their father). To put this another way, women pass on an X chromosome to both male and female offspring, where as men only pass on their X chromosome to their daughters.

The situation is complicated by the fact that sometimes a woman can pass on an X chromosome unchanged, and at other times she passes on a combination of her X chromosome pair. By applying logic one can utilise X-chromsome analysis to assist in relationship possibilities.

2.3 Y-Chromosomal (Y-DNA)

Some of the testing companies do not do Y-DNA testing . Y-DNA is only relevant for males, and is inherited from their father and passed on to their sons. The interesting thing about the Y-chromosome is that it is usually passed on unchanged, but when it mutates (rarely) it is done at a known and consistent rate. I would expect to have an identical Y-DNA to my male siblings, my son and my paternal line grandparents. This becomes very useful for paternity testing or for finding out the migration path of your paternal line.

When you do a Y-DNA test you are asked to make a decision on how many marker test you want i.e., 12, 25, 37 (usually up to 111). For a 37 marker test 37 predetermined positions along the Y-chromosome will be tested and at each position a count will be done of particular repeating DNA sequence. These are called Y-STR ("short tandem repeat") tests. These results define the person's haplotype. The haplotype of 2 males can be compared and, generally, the more similar they are, the more closely related they are.

Another series of tests that can be carried out on your Y-DNA are known as Y-SNP tests ("Single Nucleotide Polymorphism"). These determine the value (A, T, C and G) of variable nucleotides, along the length of the Y chromosome. The results of these tests help to place the test-taker on the Y-DNA haplogroup tree and indicate where mutations have occurred and hence where their most distant position on the tree is.

From the testing I have undertaken (see above) my own haplogroup has been confirmed as R-Z2109 (which puts my most common recent ancestor at about 4,000 yrs ago), and I'm hoping through more testing I can get it down to about 5-600 years. This, of course, only refers to my paternal line.

2.4 Mitochondrial DNA (mtDNA)

mtDNA is found inside most cells of the human body. Most other DNA (but not Y-DNA) gets jumbled in the "recombination" process. mtDNA is passed down from mother to child without change. It is important to note that a mother will pass mtDNA to both male and female offspring, but a male will not pass it on at all. To a large extent it is the female equivalent of Y-DNA.

This then becomes a great tool in connecting a maternal line together. Not all testing companies do mtDNA testing.

3. Testing Company Selection

I believe that the major considerations are :-

· what testing does the company do (atDNA, Y-DNA etc) and how does this measure up with your requirements

· how large is their database of test-takers and how accessible are the results

· what other facilities does the testing company offer e.g.,

o ability to import from and export results to other organisations

o chromosome browsers

o ability to load your own family tree via a gedcom file

o Y-STR and Y-SNP testing with consultant advice available

o Special interest forums

· What is the turnaround time on tests i.e., the time from providing your cheek swab (or saliva sample) until the results are available. Some are tested in Australia and some are not.

· privacy issues

My own selection was Family Tree DNA mainly because it had all the facilities mentioned above. I had significant requirements for Y-DNA testing and several of the other companies did not have this available.

One thing to keep in mind is that a testing company not having a large data base of test-takers can be overcome to some extent by migrating your results to a common DNA database facility called Gedmatch

"Gedmatch" does not perform DNA testing but it allows easy import of atDNA and X-DNA results that have been created elsewhere. It has a large database (don't know how it compares) and is very rich in facilities and is free to use. The screen handling is not "beautiful" and has a bit of an academic look and feel. Well worth using as a complement to whichever testing company you select.

I thought the following was a fair comparison of available testing companies

comparison of DNA testing companies

For those who wish to learn a little more on this topic I can recommend a publication, "The Family Tree Guide to DNA Testing and Genetic Genealogy" by Blaine T. Bettinger. I have no personal or commercial association with this publication. It is available for on-line ordering at Amazon and many other book stores.