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We investigated how to capture the genetic population structure in a well - characterized sample from the Netherlands and in a worldwide data set and examined whether ( 1 ) removing long - range linkage disequilibrium ( LD ) regions and LD - based SNP pruning significantly improves correlations between PCs and geography and ( 2 ) whether genetic differentiation may have been influenced by migration and / or selection .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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