There are 4 types of DNA for which you can receive test results: Autosomal, Y-DNA, X-DNA, and mtDNA.
To better understand the differences, it may be useful to visualize these different DNA tests and how they apply to genealogical research by looking at a family tree.
Look at a tree in “pedigree” view. The pedigree view is read from left to right. It shows the “home” person on the left side of the page, with parents branching off to the right, father on top and mother below, and then each generation continues branching off further and further to the right side of the page as you proceed back in time. Here’s my tree in 5-generation pedigree view:
The Y-DNA test focuses exclusively on the Y chromosome handed down from father to son, ad infinitum. In a family tree, this means that Y-DNA results only apply to the one ancestral line that resides on the top of the page, going from left to right, from son to father to father, and so on. In my case and my brother’s case (and our sons and grandsons), this only applies to the purely paternal Jonnes/Jones line, without factoring in any of their wives: Nelson Jonnes to Lloyd Jonnes to Howard Jones, etc. In the case of my maternal uncles, this only applies to their purely paternal Bonn/Bøn line: Bert Bonn to Bernt O. Bonn to Ole Larsen Bohn, etc.
It is important to understand that Y-DNA tests by definition will not help with any other lines. If we go back 4 generations to my 2GGs, my Y-DNA results will only pertain to one of those 16 people: Dr. Nelson E. Jones (1821-1901). If we go back 7 generations to my 5GGs, my Y-DNA results will only apply to one of those 128 ancestors: Henry Jones (1734-1806). If you go back 10 generations, there are 4,096 ancestors at that generation level (8GG), but again, only one will share your Y-DNA.
Many DNA testing company will ask you to identify your earliest known Y ancestor from your family tree once you’ve set up an account. In my case, our earliest known patrilineal ancestor is 7GG John Jones (1670?-1727) from northern Wales.
Likewise, the mtDNA test focuses exclusively on the matrilineal heritage passed down from mother to child, ad infinitum. Both sons and daughters receive it, but only mothers pass it on. In my family tree, this applies to the one ancestral line that resides on the bottom of the page, going left to right from child to mother to mother to mother, and so on. In my case, we are talking about the matrilineal line: Beverly Bonn to Helen Vermilyea to Mabel King to Lena Miller, etc. Again, it is important to understand that mtDNA results will not help with any other lines.
In my case, our earliest known matrilineal ancestor is 4GG Rosie Reist (1801-1890) from Colmar, France in Alsace-Lorraine.
X-DNA results have a unique heritage pattern because men and women differ in how this applies to their family trees. For men, X-DNA can only come from their mother; for females, it can only come from their mother and their father’s mother. There are special charts that help genealogists visualize how X-DNA can be inherited.
The Autosomal test is the big one. This applies essentially to everyone in your family tree. It tests all of your DNA from all of your ancestors except for the Y chromosome and the mtDNA found outside the nucleus.
Some people get confused because they think that Autosomal results exclude your patrilineal and matrilineal lines. They do not. Just because the Y-DNA test only applies to your patrilineal line does not mean that the autosomal test is not capturing DNA from the men in that line as well. Ditto with the mtDNA test and your matrilineal line. Remember – the Y-DNA test only examines the Y chromosome. However, our patrilineal ancestors each still had 22 other chromosomes. In other words, my Y chromosome comes from my Dad, yes. But he also passed on a ton of other genes from his 22 autosomes, some of which would have come from his father, Lloyd Jonnes, and from his father, Howard Jones, and so on.