I recently had my DNA tested and am currently navigating this scientific world of the New Age.
I am not going to advocate a particular company but I can advocate doing your research about which one is best. Do not necessarily go with the cheap option or the one you have a family tree subscription with…..
Some companies offer free uploads of data from other companies but not all. Again, do your research.
It is a fascinating area and opens up a whole new world of possibilitites in genealogical research.
If you were descended from an illegitimate child, of unknown parentage, a foundling, orphan or don’t know your family history, it can be illuminating.
However, you cannot get info on your grand/mother’s father’s line or your father’s mother’s line, unless you test that person’ DNA. The male line can be traced back, as can the female line, but not criss-crossing back and forth.
Autosomal tests produce information from both maternal and paternal lines but are ethnicity estimates only and the value in these tests in more in the links you can get by seeing the Chromosomes in common along with known information and data collected from Birth, Death, Marriage information on family trees.
Then you can upload your data to a free website called GEDMATCH to find out more relatives who share your genetic blueprint in some way or another. Fun!
The area is developing very quickly and databases of companies are growing so information they give you can only get more and more precise. Good luck!
Then you can delve deeper in to the science behind the numbers. This is copied from http://isogg.org/wiki/Identical_by_descent where you can read much more.
Something to Ponder About
Identity by descent can be considered on various timescales. According to population genetics theory all individuals have common ancestry in the distant past, and we all have short, old IBD segments in common. For the purposes of genetic genealogy the focus is on detecting large IBD segments within a genealogical timeframe (effectively within the last ten generations) where there is a possibility of identifying the common ancestor through documentary records. In general terms the larger the segment the closer the relationship, but the frequency of the segment also needs to be taken into account. High-frequency IBD segments are more likely to be a signal of distant sharing at the population level whereas a segment that is only observed in two independently sampled individuals is more likely to be IBD.
Any given pair of individuals is related through many common ancestors, though many of these relationships will be too distant to result in detectable IBD segments. If the two individuals have ancestors from the same geographical region they might have many recent common ancestors, but many of the relationships will not result in IBD sharing, and there might only be one or two segments inherited from just a few of their many common ancestors. In a study of a European subset of the Population Reference Sample (POPRES) dataset it was estimated that for the most part IBD blocks longer than 4 cM come from 500 to 1,500 years ago, and blocks longer than 10 cM are within the last 500 years.
In general it will be difficult to find the genealogical connection with the majority of your matches under about 15 cMs. Most people are unable to trace all of their ancestral lines back ten generations or so, and the common ancestral couple cannot therefore be identified. Even if a shared ancestral couple can be identified, without tracing all the other ancestral lines you cannot eliminate the possibility of shared ancestry on other as yet undocumented lines. Many matches under 15 cMs will in any case share ancestry more than ten generations ago and will be mostly beyond the reach of genealogical records.