Patterns of nucleotide variation and gene associated SNP analysis in a Quercus spp. forest at isocitrate dehydrogenase genes Genomic DNA contains the primary source of genetic information. Thus its analysis provides the highest level of genetic resolution. DNA sequencing and genotyping methodologies based on it in particular genotyping of Single Nucleotide Polymorphisms (SNPs) facilitated new research approaches in forest genetics. Both quantitative and population genetic methods are being applied to better understand the association between genotypic and phenotypic diversity and to detect the signatures of natural selection upon different parts of the genome in forest trees and their populations.Oak populations have been widely used as model species to study adaptation of forest trees in variable environments due to their wide geographical range and the large variation of climatic and edaphic condition that they occupy. Four oak species that coexist in the Bejan Oak Reserve (a species rich temperate oak forest in west central Romania) were investigated in the present study: Quercus robur Q. petraea Q. pubescens and Q. frainetto. The four species are closely related likely to hybridize and belong taxonomically to the section Quercus sensu stricto (white oaks) according to the most recent classifications. According to the geographical range of the species the site of investigation is for the two more widely spread European species (Q. robur and Q. petraea) in the centre of their distribution whereas for the two so called thermophilous and xerothermic oak species (Q. pubescens and Q. frainetto) the Bejan Oak Reserve is located at the east northern margins of their distribution ...