To test for human population substructure and to investigate human population history we have analysed Y-chromosome diversity using seven microsatellites (Y-STRs) and ten binary markers (Y-SNPs) in samples from eight regionally distributed populations from Poland (n = 913) and 11 from Germany (n = 1,215). Based on data from both Y-chromosome marker systems, which we found to be highly correlated (r = 0.96), and using spatial analysis of the molecular variance (SAMOVA), we revealed statistically significant support for two groups of populations: (1) all Polish populations and (2) all German populations. By means of analysis of the molecular variance (AMOVA) we observed a large and statistically significant proportion of 14% (for Y-SNPs) and 15% (for Y-STRs) of the respective total genetic variation being explained between both countries. The same population differentiation was detected using Monmonier's algorithm, with a resulting genetic border between Poland and Germany that closely resembles the course of the political border between both countries. The observed genetic differentiation was mainly, but not exclusively, due to the frequency distribution of two Y-SNP haplogroups and their associated Y-STR haplotypes: R1a1*, most frequent in Poland, and R1*(xR1a1), most frequent in Germany. We suggest here that the pronounced population differentiation between the two geographically neighbouring countries, Poland and Germany, is the consequence of very recent events in human population history, namely the forced human resettlement of many millions of Germans and Poles during and, especially, shortly after World War II. In addition, our findings have consequences for the forensic application of Y-chromosome markers, strongly supporting the implementation of population substructure into forensic Y chromosome databases, and also for genetic association studies.

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Minerals are among the most important substances promoting the beneficial effect of tree sap on a human body. However, the composition of tree saps is characterised by high intra-and interspecies variability and it is also known to vary in time even when collected from trees of the same species. The aim of this work was to evaluate the time-related variability of the mineral content in birch tree sap, to prove dependencies between the mineral composition and basic physical parameters of tree saps, and to refer the results obtained in our study to the Polish nutritional standards. Based on the results, it can be concluded that there is no point in time when birch sap invariably achieves superior nutritive values. This is proven by the fact that two of the three tested birch trees had a higher content of minerals at the beginning of sap collection, while the remaining one produced better sap at the end of the experiment. The differences in the mineral composition of tree saps observed during the two-week study raise doubt about the nutritional benefits of their content. For example, one liter of sap collected during two weeks from the three tested birches supplied from 8.49 to 26.34%, 0.9 to 2.80% and 9.17 to 20.23% of the adequate intake of potassium defined in the Nutritional standards for the Polish population (2013). For zinc, the recommended dietary allowance value based on the Nutritional standards for the Polish population (2013) was covered by one liter of sap in the following ranges: from 0 to 2.11%, from 0.85 to 21.50% and from 7.34 to 15.63%. Moreover, it is impossible to estimate the nutritional value of tree saps, understood as the mineral content, from the physical parameters of birch saps. The values of the examined parameters did not correspond reliably to the mineral content. Nonetheless, electrolytic conductivity may reflect more faithfully the nutritional benefits. The higher the EC in the saps from two out of the three birch trees tested, the higher the expected concentration of minerals important for humans, i.e. calcium, zinc and potassium.