Egan Families


DNA Explanation

The following excellent explanation of the DNA options come from the DNA Newsletter Facts & Genes from Family Tree DNA July 24, 2002 Volume 1, Issue 1. The Clan, at the instigation of the Mac Aodhagáin, is now running a Surname Project as recommended in this article.

What will Genetic Genealogy do for your research?

The term Genetic Genealogy refers to the application of science, through testing DNA, to uncover information about your ancestors. There are currently two types of tests available to the general public: the Y-DNA test and the mtDNA test. The Y-DNA test tells you about your male ancestors, and the mtDNA test tells you about your female ancestors.

The Y-DNA test is for males only as it tests the Y chromosome, which is only found in males and is inherited from the father’s direct paternal line (grandfather to father to son). Scientists have determined that the Y chromosome is passed from father to son unchanged, except for random mutations that are estimated to take place only once per 500 generations per marker.

The direct line of descent for males is critical. Events such as adoption or an extramarital male birth would break this chain. All males with a direct line of descent from your most distant known male ancestor should have the same Y chromosomal pattern, or genetic fingerprint, except for the random mutations. If you compare the genetic fingerprints of these male descendents today, they should match.

How can this help you in your research? Testing the Y chromosome can verify what is known. It can point you in a direction for further research, or prove or disprove a relationship or theory. Family Tree DNA’s Y-DNA test can find others to whom you are related. It might point you to a specific geographic location for further research. The individual reasons for doing Y-DNA testing vary significantly, from curiosity to specific genealogical research goals to large surname projects.

Here are just a few examples of the use of Y-DNA testing. For example, suppose two immigrants, who came to the U.S. in 1740, had the same surname, but you can't connect them. By testing direct male descendents of each immigrant, you can determine whether or not the two immigrants were related. In another situation, your family legend is that your surname was changed on immigration. All persons with the new surname found in the US fit into your tree. Your grandfather gave you two possible original surnames. By testing descendents of the two possible original surnames, you could determine if you were related to either. In another example, you have found your surname in New Zealand, and those people come from the same County in Ireland. By testing both groups, you can determine if they are related, and perhaps you will focus more research in this Irish county for paper records. In many cases, you may only need as few as two participants to apply Y-DNA testing to solving your genealogy brick walls or adding more information to your family

Y-DNA Surname Projects attempt to test all lines, branches and variants of a particular surname to determine which are related. Surname Projects can start small with a subset of the surname and be expanded in phases.

The mtDNA test is available for females and for the female ancestors of males. We all carry mtDNA inherited from our mothers. Anthropologists have determined that there exist approximately 20 daughters who are descended from a single ‘mitochondrial Eve.’ Family Tree DNA’s mtDNA tests will determine from which daughter of Eve you descend. You can then use the Family Tree DNA database to find others whom you match

How many markers should I test?

The question asked the most often by people considering the Y-DNA test is ‘How many markers are enough?’
The place to start is to define the term ‘marker.’ A marker is a location on the Y chromosome that may be tested for Genetic Genealogy. These locations, or markers, have names, such as DYS #19 or DYS #385a or DYS #439. When a marker is tested, the result is reduced to a number, which represents the number of repeated patterns of the DNA protein sequence at a specific location on the Y chromosome.

Family Tree DNA offers a 12 marker Y-DNA test and a 25 marker Y-DNA (called Y-DNA Plus) test ( a 37 marker test is now available). The difference is that the Y-DNA Plus test results, with its additional markers, reduces the time frame to the Most Recent Common Ancestor, or MRCA. For both tests, the number of markers that match can determine whether you and another participant share a common ancestor and how many generations ago that common ancestor might
have lived.

If two individual's test results match exactly (12/12) in the 12 marker test, there is a 99% probability that they are related. The issue then becomes: when did this common ancestor live? Unfortunately, science cannot pinpoint the exact generation, but science can provide a range of time when the common ancestor might have lived.

If two individuals match in the 12 marker test for either 10 out of 12 (10/12) or 11 out of 12 (11/12), they are also considered related, but the time frame to the common ancestor, MRCA, is more distant than if they had a 12/12 match. Where the matches are less that 10/12, the two individuals are not considered to be related.

If your 12 marker test results match another participant’s exactly, 12/12, your common ancestor occurred between 1 and 62 generations ago, with a 50% probability that the common ancestor lived 14.5 generations ago or less. There is a 90% probability it was within 48 generations and a 95% probability it was within 62.

You can shorten this time span by increasing the 12 marker test to a 25 or more marker test.

If two individuals match exactly (25/25) in the 25 marker test, their MRCA would have lived between 1 and 32 generations ago, with a 50% probability that the common ancestor lived 7 generations ago or less. There is a 90% probability the MRCA was within 24 generations and a 95% probability that it was within 32 generations. Therefore, increasing the markers tested from 12 to 25 lowers the time frame to the MRCA from 14.5 to 7 generations.

Clients can choose either the 12 marker test or the 25 marker test, depending on their objectives. A 12 marker test can be upgraded to a 25 marker test at a later date. The Lab used by Family Tree DNA, based at the University of Arizona in Tucson, keeps a sample of your DNA stored under a kit number. If, later in your project, you decide to expand your test to 25 markers, the additional markers can easily be tested from the DNA already stored for reprocessing

Many clients struggle with the choice between 12 and 25 markers, as wellas who to test. Our recommendations vary based on the client's objectives and situation. Examples are provided below to assist you in making your decision for the number of markers and selecting participants.


There is only one surviving direct male descendent in your line, traced back to the early 1800's with documented research. You are not ready to start a project and haven't researched other lines with your surname. You never find the time to spend to understand DNA testing. Your direct male descendent is in his late 40's.


On the surface, it appears that you have plenty of time to learn about DNA testing, and have your relative tested. Unfortunately, once this direct male descendent is gone -- you can probably never get a DNA sample. In the situation where there is only one surviving direct male descendent, regardless of their age, we recommend immediate testing.

Either the 12 or 25 marker test will do. Any time in the future, others with your surname can be approached to be tested for comparison. The objective today is to get a sample from your relative and have it tested to ensure that you will not be denied the opportunity in the future. You will then have the results for the direct male descendent, the results will be stored in our database, and the sample will be stored for your future use.

If there are as few as three direct male descendents in your tree, we recommend immediate testing of two of the males. The reason to select two is to confirm that there were no adoptions or extramarital male births. Often, it is only a priority to test males if they are elderly. The issue is not age. If the person is gone, for all practical purposes, their DNA is gone. We were able to assist a client late last year, whose only direct male descendent was killed in a car accident. Securing the sample took tremendous effort, and the involvement of the spouse for approval and the medical examiner for a sample. It was sheer luck that the client remembered in such a stressful situation, and contacted Family Tree DNA on a Saturday night at midnight, so that we could immediately overnight a collection kit.

In summary, if you have a small number of direct male descendents in your line, we recommend immediate testing of two participants, to confirm a match and to have the sample and results stored for future reference. If you do not get an exact match, expand the testing to any remaining direct male descendents to determine where and when a non-paternity event occurred, such as adoption.


Two immigrants came to the U.S. in 1740 with the same surname. Extensive research has occurred, but you can't connect them with paper records. There are many descendents today in the U.S.


Our recommendation is to test two direct male descendents from each immigrant's line for 12 markers. The rational behind this recommendation is that there is large span of years between the immigrants’ arrival and today, as well as many birth events that provide an opportunity for an extramarital male birth or an adoption. By selecting two males from each line, you would expect a match within each line to validate the results. Then, when you compare the results from the two lines to each other, you would be confident that you have accurate results.


You are interested in determining which lines with your surname are related. Your surname can be found in England, Ireland and the U.S. You have extensive paper documentation on your line and contact with one researcher in England who has researched their line. This other researcher has also identified nine separate trees with this surname.

Where and how do you start?


You are an excellent candidate for a Surname Project. A Surname Project can be established with a minimum of six participants. There are two primary approaches, depending on the size of your Surname Project and the extent of the paper genealogy records. For a relatively rare surname, with limited descendents and excellent genealogy records, we recommend testing one or two direct male descendents from each line for 12 markers.

If matches occur, you may want to expand to 25 markers. When no match occurs between two the lines, we recommend that an additional direct male descendent be tested in each of those non-matching lines.

For surnames that are not rare and have many branches and descendents, we recommend testing two males from each line to establish the genetic fingerprint. (Remember: In every generation, the opportunity for an extramarital male birth or adoption exists). Where no match occurs, expand the testing in the two lines that do not match to include an additional male in each line.


In conclusion, the situations and objectives vary between families. The examples provided above may help you determine what approach to take with your DNA testing. If you are not sure of your objectives, and want to
get started, our recommendation to clients is to select the 12 marker test, and to later upgrade to the 25 marker test when a match occurs, to reduce the time frame for the common ancestor, MRCA.

Citation: Copyright 2002, Family Tree DNA "Facts & Genes" (

Clan Egan DNA Project

Clann Mac Aodhagáin Australia & New Zealand
Copyright © 2000-2023 Clann
Mac Aodhagáin (Australia & New Zealand)- All rights reserved. Last updated November 2023.