Mark discussed Y-DNA and mtDNA. If you are interested in finding out information on the male line of the family then you test the Y-DNA, for the female line then you test the mtDNA. Now having said that, men can test their Y-DNA and women can't since we don't have a "Y" chromosome. The "Y" being the gene that has been passed down from father to son through the generations. This is only the men, so by doing this test you will not find out anything about your great grandmother on your father's side. The "mt" part is inherited from your mother. By testing this part you can find out about the mothers in your line on your mother's side. Women can only test their mtDNA, but men can test both. Mark also mentioned a test for Autosomal DNA. This can give you some information on both parents and is a new test being offered by Family Tree DNA.
Family Tree DNA is the company that has the largest database in the U.S. and outside of the U.S. it is Roots for Reel. Mark suggested to start with a 12 marker test and then upgrade to a 67 or 111 marker test, as that may be more cost effective. The higher the marker test you get the more specific the results will be.
When the lecture was over my hands were itching to get a hold of microfilm and do some research. However, after being away all week I wanted to spend time with my boys and husband. So it was off to Chuck E. Cheese's for me with DNA on my mind.