Polyploidy, or whole genome duplication (WGD) occurs in virtually all vascular plants and has played a major role in evolution. Here we leverage the recent developments in sequencing technology and previous studies in the Capsella genus to characterize genomic and expression changes associated to WGD in C. bursa-pastoris, a recently formed tetraploid weed. C. bursa-pastoris is an allotetraploid of C. grandiflora and C. orientalis. We will first conduct whole-genome resequencing and then gene expression studies of the three species. In the case of C. bursa-pastoris, we will analyze accessions from three genetically and phenotypically well differentiated regions, Europe, Middle East and China. The C. bursa-pastoris data, together with data from its two diploid ancestors, will be used to assess changes associated to WGD. The availability of data from three regions within C. bursa-pastoris will allow us to assess the predictability of these changes. These data sets will be used to address questions about the genomic consequences of WGD between species and between populations within species: Which genomic regions have been deleted after WGD and are some functional groups more affected than others? Has WGD led to genome-wide relaxation of natural selection in polyploids? Do gene duplicates resulting from WGD evolve more slowly than singletons? Are evolutionary rates correlated to differences in expression levels and patterns?