A striking feature of the plot is the distinctiveness of the different Finish samples (light vs. dark brown points). This is not so difficult to explain if one considers that the light brown squares (DGI-FIN) are from Botnia. This parallels the results of Salmela et al. (2008) or Jakkula et al. (2008) in underscoring the internal structure of the population of Finland
The familiar V shape was also observed in the PCA produced by McEvoy et al. (2009) or Nelis et al. (2009). In my opinion, it is produced by the differential representation of the two main population elements of the Nordic countries, namely the Germanic and Finnic elements.
Here is the website of NordicDB.
European Journal of Human Genetics doi: 10.1038/ejhg.2010.112
NordicDB: a Nordic pool and portal for genome-wide control data
Monica Leu et al.
A cost-efficient way to increase power in a genetic association study is to pool controls from different sources. The genotyping effort can then be directed to large case series. The Nordic Control database, NordicDB, has been set up as a unique resource in the Nordic area and the data are available for authorized users through the web portal (http://www.nordicdb.org). The current version of NordicDB pools together high-density genome-wide SNP information from ~5000 controls originating from Finnish, Swedish and Danish studies and shows country-specific allele frequencies for SNP markers. The genetic homogeneity of the samples was investigated using multidimensional scaling (MDS) analysis and pairwise allele frequency differences between the studies. The plot of the first two MDS components showed excellent resemblance to the geographical placement of the samples, with a clear NW–SE gradient. We advise researchers to assess the impact of population structure when incorporating NordicDB controls in association studies. This harmonized Nordic database presents a unique genome-wide resource for future genetic association studies in the Nordic countries.