Genetics of England at least are predominantly Anglo-Saxon which we tend to treat as the starting point. You do have to fudge the data a bit to see it but a stu

Genetics of England at least are predominantly Anglo-Saxon which we tend to treat as the starting point. You do have to fudge the data a bit to see it but a study took English people whose family since their Great Grandparents lived within a 100 mile radius (i.e. non-migratory) and found their genetics were very predominantly Anglo-Saxon... or well at least over the dataset homogeneous to a point (the assumption being Anglo-Saxon). The historic cut off points of Scotland, Wales and Cornwall are clearly demonstrated in the genetic data which lends it some credence as that was the reach of the Anglo-Saxon invasion.