YDNA- Y chromosome DNA - Paternal line
YDNA stands for Y chromosome DNA. The YDNA is what makes a man, a man. The YDNA then, can help you trance a direct male line. Only males can take a YDNA test, so ladies, that means you have to use your powers of persuasion to get the men in your life to take this test.
This test works because the YDNA is directly paternally inherited. That means that living men today have the same, or very similar, YDNA as their father, grandfather, great grandfather, and so on.
You can only order the most genealogically valuable YDNA test from one company: Family Tree DNA. They have three testing levels starting with 37 markers and moving up to 111 markers. In general, you can start with the 37 marker test as it is usually enough to tell you if you are, or are not related to someone. The 67 and 111 tests can then help to further refine your relationship. You can always upgrade later without resubmitting a sample (just pay them more money!).
If you match with someone on a YDNA test then you likely share a ancestor with that person along your paternal line. This short video explains paternal line inheritance.
The YDNA Test Gives You Two Types of Results
Your haplogroup is your deep ancestral group. And when we say deep, we mean deep. Your haplogroup tells you where your ancestor was up to 10,000 years ago! It is named with alternating letters and numbers, and most often just identifies a very broad geographic area of origin.
Matches are other people who have tested their YDNA and have values that are the same or very similar to yours. It is possible that these people share a common paternal ancestor with you. Which means that if you were to look at your father's father's father father and your match's father's father's father father, you would eventually find the same guy.