Whole-genome duplications (WGDs) in plants and other organisms are important evolutionary events that have been linked to survival of ecological catastrophes, increased speciation, expansion of the regulatory repertoire of species and evolutionary innovation. But many questions concerning the involvement of WGDs in these processes remain unresolved. We propose to study the impact of WGDs on plant diversification in more detail. We will make use of a peculiar reciprocal relationship in the duplicate retention pattern of certain dosage-sensitive gene families to identify WGD marker gene families whose evolutionary expansion parallels the WGD history in the angiosperm lineage. Experimental screening of marker family size variations across a large number of strategically placed plant species will allow us to pinpoint the phylogenetic position of known WGDs in particular plant clades and study the relationship between WGDs and speciation/morphological diversification in more detail. Additionally, we will screen unexplored plant clades for evidence of as yet undiscovered WGDs and try to confirm our previous observation that there has been a wave of WGDs in angiosperms around the K-T boundary. Finally, we will investigate links between the expansion of particular dosage-sensitive gene families and evolutionary innovations or elaborations in diverse angiosperm lineages.