probably about half or more of Manx who can trace back to Island families of early 19th C before the significant arrival of English settlers will have Scandinavian genes in their DNA as IoM was an important part of their 'empire' (read up about Kingdom of Man and the Isles); since they arrived in this area from a little before 900AD then you have 700 years of unrecorded family history before you are on even shaky Manx genealogy.