Why do matches from one part of the family show up and others never do?

[Chrisinhouston]

I have a very good working knowledge of my ancestry and an extensive family tree; I a have been working at it for almost 20 years. I have done the FF test here at FTDNA as well as Y67 mostly to verify what I know but also to look for the unknown. I have discovered a few first and second cousins, mostly children born to unwed mothers in my family and put up for adoption.

But he majority of "Matches" are on my mother's maternal grandparents side. Both of my mother's maternal grandparents from Sweden and came to the USA in the 1880's and I seem to have so many matches to people either in Sweden or Scandinavia. But I don't seem to have any that I can be sure of on mom's paternal side which was Luxembourg and Belgium. Do Swedes just do DNA testing more?

And on my father's side I have found matches for his father's father's line but nothing on my father's mother's side. My father's maternal grandmother was Japanese, and I am 1/8 or 12% Japanese/Eastern Asian which the "My Origin's" map confirms but I have no matches showing up who are Japanese. Does that mean DNA testing hasn't caught on in Japan?

[John McCoy]

I expect you are correct, your set of matches is strongly influenced by who has tested. The Family Finder test is overwhelmingly more popular in the US than elsewhere. In some parts of the world, there are actually regulations that make it difficult or impossible to obtain and ship DNA samples. Also, there are or have been large Scandinavian communities in the US, and they have been very active in genealogy, perhaps because of the challenges (and rewards, when you succeed) involved in finding your cousins under a patronymic naming system.