Since the genetic variation is of great importance for the choice and conservation of forest gene resources, the problem concerning the most suitable categories of trait for determining and quantifying genetic diversity within and among populations was discussed. While describing the properties of the various categories of trait, it became evident that molecular markers (isozyme and DNA markers) are most suitable for discovering allelic variation at individual gene loci. From the perspective of gene resource conservation, the genetic and molecular properties of the different markers are outlined and their possible use for conservation purposes discussed. Based on these considerations, conclusions are drawn, which may be worthwhile for forest gene conservationists.