17 June 2010

Three DNA Tests for Genealogy, part 1 Overview

Over the course of the next few weeks, my posts will be a series on the new austosomal testing for genealogy. The first three parts in this series reviews some basic facts and clarifies the three types of testing for genealogy. The next section will explore the various aspects of autosomal testing for Family Tree DNA's Family Finder. Much of this information applies to any autosomal testing for genealogy; however, company offerings do vary and that topic will conclude this massive series.

These articles are meant for the Newbies and those interested in a basic understanding. They will not get over technical.

All material is under copyright. Please write directly for permission to use any information. Email: aulicino@hevanet.com

Part 1:
- Historical background and a few facts

Family Tree DNA pioneered DNA testing for genealogy in 2000, bringing the power of DNA tests to family historians. In the years since, family history researchers who use DNA tests have become known as genetic genealogists. These dedicated researchers understand the value of DNA testing as being the most accurate tool available.

The first years saw rapid changes in our understanding of the science and improvements in the power of available tests. In early years, only a few Y-chromosome STR (short tandem repeat) markers were available. Today it is routine to test with 67 STR markers. Mitochondrial DNA (mtDNA) started with the humble HVR1 test. Now the entire gene sequence is standard.

It looked as if little more could be done for family researchers, as early autosomal testing was neither accurate nor reliable enough for genealogy. That has changed. We are embarking on a new adventure, a new stage in DNA testing, and once again we have become the pioneers for this new generation of DNA testing.

However, I find that many genealogists and other interested parties, as well as some genetic genealogists, are confused about the three types of tests: Y-DNA STR, mtDNA full genomic sequence, and autosomal microarray. Simply put, the Y-DNA test gives you results along the very top line of your pedigree chart, the mtDNA gives you results along the very bottom line and your chart, and now the autosomal test gives you matches on all the lines between the top and bottom. Each test is important for different reasons, and this series will help you understand all three by comparing their basic concepts.

The Facts

We know that all of mankind is closely related. With each generation we double our ancestors, giving us a billion ancestors in thirty generations. The population of the earth thirty generations ago was no where near a billion people; therefore, we are related to ourselves many times over due to what is called pedigree collapse. Pedigree collapse is the reduction of ancestors given that cousins marry; that is, if two first cousins married, they would only have six grandparents and not eight. The farther you go back in time, given that people tended to remain in one area, more and more cousins married. We may have a billion ancestors in thirty generations, but they are not a billion different people.

We share 99.9% of our genome with all other humans. We have about 3 billion base pairs in our genome, and about 98% of those are loosely called Junk DNA as scientists have yet to discover their purpose.

We have 22 pairs of chromosomes and the sex chromosomes (Y and X). Men inherit the Y-chromosome from their fathers and one X chromosome from their mothers. Women inherit an X from each parent.

We know that every DNA test provides you with a set of numbers or numbers and letters, giving you a DNA signature (your results). Those testers who match your signature are related to you at some level.

We know that any DNA test will not tell you the name of a common ancestor or when and where that ancestor lived. It is up to good genealogical research to make that determination.

As genealogists, we know to use the right source or sources to find an ancestor's information. If we are looking for an ancestor in Britain, we do not search the US census. When we are looking for that ancestor's married name, we know that the census will not help. We know instead to consult vital and church records according to the time and place. We use the sources that may provide the information we need. The same is true for using DNA for genealogy. The three types of DNA most commonly used are the Y-chromosome DNA (Y-DNA), mitochondria DNA (mtDNA), and autosomal DNA (atDNA). Each is used to find others who are related to us, but each one is used to find matches in different parts of our pedigree chart.

Before we move forward, we must understand each test's strengths and weaknesses. The next article in this series will explain the difference between the Y-DNA & mtDNA test.

copyright 17 Jun 2010, E. Aulicino
Thanks to R for editing assistance.

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