There are three (3) different types of DNA test available to further one's genealogical research. These are: yDNA, mtDNA, and atDNA. The type of test you take should be ordred on the specific question you want answered. For the purposes of surname studies one would order the yDNA test. Only men can take the yDNA test. The atDNA (autosomal DNA) test uses the DNA you get from both sides of your family and is useful in connecting you with living relatives with whom you share a common ancestor within the past 5 - 6 generations. Both males and females carry mtDNA inherited from his/her mother. mtDNA traces the maternal line only. While it is not useful in surname studies, mtDNA does trace your deep ancestry inherited from your maternal line.
DNA test results are best used in combination with traditional paper-trail research. All three types of DNA tests can assist you with your family research by confirming things you already know as well as connecting you with living relatives with whom you can collaborate. In addition, information about your genetic makeup and the ancient migratory patterns of how your ancestors travelled throughout time can provide clues for current areas of research.
The yDNA test is for men only. Females wishing to research a specific surname need to secure the cooperation of a male relative to participate in a yDNA test. The yDNA test uses markers on the y-chromosome, which are passed from father to son unchanged for generations. All men who share a "common male ancestor" will carry essentially the same yDNA.
Both men and women can take the mtDNA test. However, only females pass their mtDNA on to their children; consequently this test is only useful in testing the participant's mother's mother's .... mother's line. Additionally mtDNA testing can help identif living relatives who mtDNA is similar to yours, as well as providing information of the ancient migration routes of your maternal ancestors.
Autosomal-DNA (atDNA) testing finds relatives across all your family lines. Both men and women can take the atDNA test. Testing of the 22 autosomal chromosomes provides comparative data between testees. The degree of matching yields scientific evidence for the estimated relationships. It is possible to discover connections to descendants of all 16 of your great-great-grandparents.