DNA testing is useful where parentage is unknown such as in the following cases:
Other situations where DNA testing is useful is where parentage is known but records are unavailable, and where the ethnic heritage of ancestors is unknown. It is generally useful in confirming that the ancestors found through researching your family tree are indeed your ancestors. If researching all the descendants of an ancestral couple, DNA testing may reveal additional relatives not found through the usual genealogical methods.
DNA inheritance is random. In the worst case scenario you may not have inherited DNA from a grandparent. In the best case scenario with autosomal testing you may be able to confirm ancestors going back eight generations. It should be noted that the further back you go through the generations the more likely you are to have a non-paternity event (NPE) or misattributed paternity; the incidence of this is said to range from 1% to 2% per generation.
The benefits of having an autosomal DNA test are twofold: an ethnic heritage estimate and a list of people who are DNA matches.
An autosomal DNA test is useful in providing an ethnic heritage estimate. This changes over time as the DNA companies' test groups become larger and from more diverse areas in the world. In addition to ethnic mix an autosomal DNA test can narrow down specific areas where one's ancestors have lived. On AncestryDNA this includes Victoria, Australia (European and British Settlers).
An autosomal DNA test will provide a list of people who are DNA matches. It will provide data on the amount of shared DNA for each person and an estimation of the degree of relationship. As the amount of people getting tested with the DNA company increases with time the number of DNA matches will increase.
AncestryDNA results include information about one's geographic origins across 1000+ regions and identifies potential relatives through DNA matching to others who have taken the AncestryDNA test. DNA test results are downloadable. AncestryDNA has the largest DNA database.
FINDMYPAST AND LIVING DNA
Findmypast has partnered with Living DNA. They also accept uploaded autosomal DNA tests from AncestryDNA, 23andMe, MyHeritage DNA and Family Tree DNA. They will map DNA results across 150 global regions including 21 in Britain and Ireland.
MYHERITAGE DNAMy Heritage DNA reveals your unique heritage - the ethnic groups and geographic regions you originate from. It will also assist you to find new relatives you never knew existed through your shared DNA. My Heritage DNA accepts uploaded autosomal DNA tests from other providers. MyHeritage DNA is said to be used more by Europeans and South Americans.
Their Ancestry + Traits Service helps you understand who you are, where your DNA comes from and your family story. They analyze, compile and distill your DNA information into reports on your Ancestry Composition, Ancestry Detail Reports, Traits, Haplogroups, and Neanderthal Ancestry. They also provide a DNA Relatives tool to enable you to connect with relatives who share similar DNA, and an automatic Family Tree builder. 23andMe has the second largest DNA database.
FAMILY TREE DNA
Family Finder DNA Test includes
myOrigins - mapping tool that provides a detailed ethnic and geographic breakdown of where your ancestors came from connecting you to regional origins from our 90+ Population Clusters.
ancientOrigins - tool that maps your ancient ancestors' migration routes and shows the amount of autosomal DNA you still carry from ancient European civilizations.
Family Matching - enhanced feature that enables users to sort confirmed DNA matches by maternal and paternal lines
Family Tree DNA accepts uploaded autosomal DNA tests from 23andMe, AncestryDNA and MyHeritage DNA.
Gedmatch is a US online service to compare autosomal DNA data files from different testing companies. GEDmatch users could upload their autosomal DNA test data from commercial DNA companies, with or without a GEDCOM file, to identify potential relatives who have also uploaded their profiles. Tools available on the GEDmatch site included sorting results by the closest matches to a user's autosomal DNA, whether one's matches match each other, genetic distance calculator, estimated number of generations to a common ancestor, whether one's parents are related, and an ethnicity calculator.
DNAGedcom is a third party tool used by genetic genealogists. The tools and documents are primarily for the use of adoptees looking for birth family.