Phylogeny of evolutionary relationships of sequenced grass genomes. Radiation of grass family, poaceae is dated to have occurred 70-50 million years before present, in line with the date for the pan-grass’ shared ancient whole genome duplication. Soon after the Panicoideae (Zm-Sb) and Ehrhartoideae (Os-Bd) clades diverged, Os and Bd diverged (~49MYA). Zm and Sb diverged ~11MYA, followed immediately by a specific whole genome duplication event in Zm’s lineage. Red stars indicate whole genome duplication events. Expanded genome phylogeny of sequenced grass genomes. Given the pre-grass whole genome duplication event and the Zm specific whole genome duplication event, there are 10 effective genomes for the 4 sequenced grass genomes: 2xBd, 2xOs, 2xSb, 4xZm. Each of these whole genome duplication events contemporaneously creates a duplicate copy of every chromosome and all the underlying genomic features and genes. However, over evolutionary time, many duplicated genes are lost from one homeologous region or its partner through a process known as fractionation. Red stars indicate whole genome duplication events.
