Identification of unitary gene loss in Poaceae species. (a) An example of unitary gene loss identification in sorghum. Orthologous genes are absent in sorghum but present in all other Poaceae species and all three out-group species; therefore, a candidate unitary gene loss event has been called in sorghum. In addition, orthologous genes in other species are regarded as orthologous counterparts of the lost gene. (b) Number of unitary gene loss events, including relic-retaining and relic-lacking ones, in four species of Poaceae, i.e., brachypodium, rice, sorghum and maize. (c) The entire pipeline for unitary gene loss identification. The number of candidates retained at each filtering step is shown.