There is a great article on Slate magazine by my favorite genetics blogger, Razib Khan. I read his posts daily on Gene Expression and it is nice to see him on something that will get his erudite writings on a complicated subject to a larger readership. The article is titled, Which Grandparent are you most related to?, and Razib proceeds to explain how you are not related to each of your grandparents equally and how you can go about testing that with a test from the company 23andMe.
The short of why you are not related to your grandparents equally goes back to Mendelian genetics, which states that you get half of your genome from your father and half of your genome from your mother. But that does not mean that you are getting exactly a quarter from each grandparent. The process is random so you most likely get a different percentage from different grandparents. You could also get nothing from some of your grandparents being that there is a 1 in 4 million chance you could get all of your maternal or paternal chromosomes from just one grandparent.
The advantages of knowing this is not trivial but can lead to a better understanding of deleterious genetic conditions that you may inherit from your parents or grandparents. Check out the article to read more.