This is from pages 276-277 of HISTORY AND GEOGRAPHY OF HUMAN GENES,
by Cavalli-Sforza et al:
"This island was settled beginning in A.D. 874, according to
tradition, by western Norwegians from the region between Trondheim and
Bergen..."
"In earlier genetic analyses (Bjarnason et al. 1973), it became
clear that, for blood-group ABO, Icelanders were more similar to Scots
and Irish than to Norwegians; the hypothesis was proposed that the
population of Iceland was mostly of Scottish and Irish origin, perhaps
because the original settlers made many slave raids in the British
Isles.....It has become increasingly clear, however, that ABO data are
not necessarily as reliable as one would like them to be for assessing
ethnic origins. They are known to be subject to natural selection for
some infectious diseases..."
"However, when a large number of markers were tested and data from
Ireland or Scotland were taken from provinces that were less frequently
settled by other Scandinavians (Wijsman 1984), western Norwegians showed
the greatest similarity to Icelanders.
"In our data, the population closest to Icelanders is that of
Norwegians (distance, 0.0074) followed by the English (0.0076), Belgians
(0.0079), and Danes (0,0088). The distance from the Irish is 0.0099,
from Scots 0.0112, and from central Europe, a somewhat higher average."
On page 271 we see a map of areas of sharp genetic change. One
of them shows a sharp genetic change between Scotland and the Orkney and
Shetland Islands, which were settled by vikings. Another is between
Ireland and Iceland.
On page 27 is a map of pigmentation of hair and eyes. All of
Norway except Lapland is in the lightest shade, as is all of Iceland.
None of Ireland is in the lightest shade. The only parts of Britain in
the lightest shade are northeastern England, northern Scotland and the
islands north of Scotland. We know from history that
vikings settled in northern Scotland, the Shetland, Hebrides and Orkney
Islands, and Danes in northeastern England. We would expect genetic
similarity between the Orkneys and Iceland.
http://www.delphi.com/nordichistory1
http://www.delphi.com/paleogenetics1