ALL YOU NEED TO KNOW ABOUT DNA
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Every cell in your body has DNA. DNA is a cluster of chemicals made up of thousands of segments. Each segment has a specific configuration which is called a gene. Before you are born it is those genes that determine the make up of your body. Certain genes are passed down from parent to child and some of those hereditary genes can be used for genealogy research. If your hereditary genes match someone else's hereditary genes you may be related.
A DNA laboratory can test cells from you body and identify your genetic genes and assign a unique number to each different gene that is called a "marker". Following are the results for one person's DNA test that shows the genetic markers.
 Only a few are used genealogy research and each of those genes has an alpha-numeric name. The first one in the above DNA results is named DSY19a. Everyone has the above genetic genes but the marker numbers for each gene are not the same for everyone. Some of the genes in the above example do not have a marker number because is not always possible for the laboratory to determine the marker number for every gene.
If two people have their DNA tested and compare their results they can determine if they might be related. If less than half of the marker numbers match it is highly unlikely that there is a biological relationship. If all, or almost all, of the marker numbers match then it is possible, but not for sure, that two people are related.
When one pays for genealogical DNA testing there is generally a choice of the number of hereditary genes that are tested and the cost of the test varies with the number of genes tested. The minimum number of genes tested is usually 12 and the maximum number of markers tested is usually 67. The more genes tested the better the change of finding a genetic match. The testing cost varies from about $50 to $400.
Having less that 15 markers tested is of little use. It will only give you an idea of the region of the world for your distant ancestors. A 30-45 marker test is the most common and it can provide information that might allow you to make a connection with someone else who had a comon ancestor. A 67 gene test is currently the best one available and provides the best results. DNA testing can indicate your ethnic makeup (Native American, Jewish, etc.) but it may take more expensive ethnic DNA testing to be sure.
An important thing to know about genealogy DNA testing is that your results can obviously only be compared with the results of someone else that has already been tested. If no one with a common ancestor tree has been tested you may not get any useful matches.
It is, of course, not possible to get a DNA sample of dead ancestors but if someone else matches you're DNA and both of you have reliable family trees it may be possible to find a common ancestor. Therefore, your matches depend on family tree information that you and possible relatives have available.
You may find that find that you have good matches with surnames other than yours. Surnames only came into use less a thousand years back. When they came into use it was common for a son to be known by a different surname based on his profession, where he lived, or something else about him. For example, James Bergmann could have had that last name because he was a miner and his son could be called James Fielder because he learned to play a fiddle. Scandinavians added "son" or "sen" to a son's first name so Claus Jacobsen's son Eric became Eric Claussen. This practice was still sometimes used into the 1800's. Another thing to consider is that non-English speaking immigrants often had the spelling of their surname changed by immigration officials. There is, of course, the possibility that you did not know you were adopted or that you unknowingly had a one parent that was not a biological parent.
Genealogical DNA testing is a relatively new thing and as an extremely small percent of the world's population has been tested the chances of finding a useful match are slim. I estimate that as of late 2009 less than 0.002% of the world's population has been tested and they are not all in the same database. It is possible, but a long shot, that you will find a living person that has good family tree information that will provide you with information you did not already have. If you can afford it, it is worth while as you may get positive results and adding your DNA to a database may help someone else.
Even a perfect DNA match and the same surname do not absolutely prove a relationship. Also, a DNA mismatch between two people with decent genealogical paper trails does not mean there is not a relationship. Genes sometime mutate so the genealogy genes of a child are not always exactly the same as the parent and this may occur in several generations. This is truer for the female side than the male side. Therefore, a relationship can only be truly established by following the paper trail of both persons to determine if a relationship is reasonable. DNA is not a substitute for conventional genealogy research but most reach a point in their research where additional ancestors can not be found. Then you have to start using the "preponderance of the evidence" method to find an ancestor and DNA testing is a tool that may help.
To trace the male (paternal) line of a family tree the DNA sample has to be submitted by a male that is believed to be a biological descendent and it is best to test the oldest living generation of the family. If you are not a male and want to test your paternal (male) heritage a biological male cousin can submit the DNA sample. The paternal tracing test is called a Y-chromosome or Y-DNA test as the Y-chromosome is passed down from father to son. The Y-chromosome test will not provide any information about your mother's (maternal) heritage.
Mitochondrial DNA (mtDNA) is passed down to both sons and daughters of mothers so either sex can submit a sample for tracing the female (maternal) side of the family tree. Maternal (mtDNA) testing general costs about twice as much as the Y-chromosome (paternal) testing. A male can pay even more and have both the male and female sides tested. A person's mtDNA can change slightly with each generation so it is not possible to determine the closeness of relationships as well as it is for Y-chromosome testing. Even with Y-DNA it is possible for a gene to mutate which will result in an incorrect marker number for that gene. Some do not consider mtDNA testing to be very useful.
Most DNA test kits include three swabs which have to be rubbed against one's inner cheek in three different places. That scrapes off enough cells for the DNA testing. The swabs are put in a supplied envelope and mailed to the lab. It usually takes 3 or 4 weeks to obtain the results.
You DNA testing company will usually provide access to a database of others that have been tested and will provide a DNA results report that includes the following information items.
1. Genetic Matches
This reports lists others that have been tested that may be related and indicates how closely the relationship might be (see item 2 below). They list the closest possibilities and there may be no one else in the database that is a really close match. Following is a sample genetic match report.
 The marker numbers are for the person that had their DNA tested. It was a 33 marker test but only 30 of the genes resulted in valid marker numbers. The check marks are for another person in the database that was listed for a "Find Match" search. The MRCA number of 7 indicates that the two are separated by 7 generations (about 175 years or 25 years per generation). There is no way to know the exact number of generations so the MRCA number is just an estimate. This genetic match report is from ancestry.com who rates it a close match but with only 18 of 30 markers matched, a separation of 7 generations, and a different surname a relationship is actually very unlikely.
Below is comparison from ysearch.org that show a perfect match for all tested markers for the person on the top line. The person on the second line had more markers tested which accounts for the blanks in the top line. In this case the two people communicated and were not able to find a connection even though it was a perfect match for the top person. If the top person would have had more genes tested it could be better know if there was a likely connection. It is best to have as many tested as you can afford. In this case the surnames did not match, if they had matched a relationship would have been likely.
 2. Genetic Distance or Number of Generations
When you do a genetic match search the results will usually indicate how many generations back there is a possible connection or a genetic distance number. Genetic distance is a mathematical calculation of the degree of genetic difference and is not the same as the number of generations. In both cases the numbers are one indication of the closeness of a possible relationship. Remember that the closeness shown is only a possibility and some results are overly optimistic in their closeness ratings.
For both the number of generations and the genetic distance numbers the number of markers that matched has to be considered. If all, or most, of your markers match those of a person who is less than about 10 generations away or a genetic distance of less than 5 there is a chance your are related. The more markers that match and the lower the generation/genetic distance number the more likely it is that there is a relationship. It is also more likely if there is a surname match.
3. Haplogroup
Haplogroups have been defined that indicate a major branch of the overall human family. Haplogroups identify the early migrations of population groups and are usually associated with a geographic region. Following are some examples of the different Y -DNA haplogroups and indicate where your distance male ancestors may have originated. The mtDNA have slightly different groups.
There are also haplotypes which are a farther division of the haplogroups.
DNA TESTING SERVICES
Who you use for your DNA testing is important from several aspects. You want it done by a trusted lab, you don't want to pay too much, and you want the results to be compared to a large database of others that have been tested. Following are two good sources for DNA testing.
This is one of the more expensive services but they are one of the oldest genealogy testing services and have a large database. They also have surname groups that can be useful but you have to use their testing service to participate in the surname groups. Their 37 marker test is adequate but the 67 marker test is the best one available.
They are associated with ysearch.org.
You do not have to be a member of ancestry.com to use their DNA testing service. They are one of the less expensive sources. Their 33 marker test may be adequate but the 46 marker test is better. You do have to be an ancestry.com member ($300 yearly) if you want to join a surname group or be able to search their regular genealogy database. You can save money by using their testing service and then manually entering your gene marker results in the free DNA databases listed below.
This is a medium priced service.
They are associated with ybase.org.
This is a medium priced service.
They are associated with the Sorenson Molecular Genealogy Foundation.
FREE DNA DATABASES
Following is information on free DNA databases that allow you to input your gene marker information and increase the possibility of finding a good match. If you use a testing service other than theirs you can manually input your gene marker numbers and get the benefit of their data base.
ysearch.org (male line only search)
This is a free database service provided by familytreedna.com.
Note, check the conversion rules as some marker numbers may have to be changed.
ybase.org (male line only search)
This is a free database service provided by dnaheritage.com.
Note, check the conversion rules as some marker numbers may have to be changed.
smgf.org (for male line search)
smgf.org (for female line search)
Sorenson Molecular Genealogy Foundation - one of the oldest.
Note, be sure to select the source for your DNA results.
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