Whole genome duplications (WGDs) are believed to play a major role in angiosperm evolution. Previous studies have found that some functional categories of genes, including regulatory and developmental categories, expand almost exclusively through genome duplication, likely because their expansion through small-scale duplications is counteracted by dosage balance effects. However, the duplication dynamics of individual gene families have not been studied in detail. We developed a stochastic birth-death model to study the size evolution of gene families across a species phylogeny, taking into account both small-scale and large-scale duplication events. We use this model on a set of angiosperm species with known WGD history to assess the dosage balance sensitivity of individual gene families, and we interpret the results in the context of the potential impact of WGDs on evolutionary innovation in angiosperms.