Skip ahead to 13:00.
What does this big recent genetic study tell us about the nations of Britain? The whole island was originally populated by Britons before the arrival of the Romans.
The Anglo-Saxon impact on Britain makes up about 10 to 40 percent of English DNA. The Viking impact on the Orkney Islands was about 25 percent of Orcadian DNA and was much more limited elsewhere. The Romans appear to have had no genetic impact on Britain.
Does that mean the English, Scots and Welsh are mostly Britons of Celtic ancestry? It doesn’t appear that way. It looks like the Celts who migrated from the continent may have had a smaller impact on Britain than the Anglo-Saxons. The vast bulk of our ancestry comes from the Bell Beaker culture that expanded into Britain from Central Europe around 4,500 to 4,000 years ago and exterminated the Neolithic people who previously lived there.
The English and Danes had only diverged about 400 years before the Viking Age which makes it difficult to tell them apart. Similarly, the Britons and Anglo-Saxons had only diverged around 2,000 years before from the same group that populated Northwestern Europe.
Note: In a nutshell, this is why it was so easy for America to assimilate closely related European groups. It takes a liberal to tell you that there is no difference between assimilating and integrating a German and a Somalian.