Certainly one of my go-to spots on the internet, Ghost of a Flea links to a story on Frisian DNA and how it tells a tale of the Angl0-Saxon (Germanic) invasion of Britain.
The linked article in Der Speigel says that Brits are more Germanic than they realize, and that “Frisian” DNA marks much of eastern England.
Fine, to a point. Unfortunately, the story appears to discuss the Frisian Modal Haplotype (FMH) identified by Stephen Oppenheimer in his “Origins of the British”. Oppenheimer only used six Single Tandem Repeats (STRs) to form this grouping, and he also put this group in Iberia during the last Ice Age, having since expanded northward into northern Europe. All work and theories under which, if you ask me, a line has been drawn. [PS, I own the book and have read it; discussed here.] That said, Oppenheimer’s discussion of the archaeological evidence for a large-scale Angl0-Saxon invasion led him to think of it as more of an incursion and a conquest of a new ruling class. [It would appear to have been more than that.]
Speaking of DNA, the research of Single Nucleotide Polymorphisms (SNPs) shows that the ‘Celtic’ markers — that is, the R1b-P312/R1b-L21 markers — are prominent throughout Britain. The SNP that would be most associated with Frisian and Germanic peoples would be R1b-U106.
The above map shows R1b-S21 (i.e. U106) distribution in modern-day Europe. U106 and P312 are two major sister clades of the R1b haplogroup [or, ‘brother clades’, I suppose I should say]. The L21 or ‘Celtic’ group came out of P312.
There is clearly an Anglo-Saxon impact, and it appears to be about 20-40% of the population of eastern and central England. But this is much lower than the levels suggested in the Der Speigel article. As it stands, there are people with verified R1b-L21 SNPs, that is, they are of Celtic descent, yet who are classified under an Oppenheimer-esque FHM group based on a mere six STRs. So, using that kind of methodology, you would tend to include people who might have similar STRs (they came out of the same R1b father clade, of course) but whose lineages split four or five thousand years ago.