Structural genome evolution model for barley from a rice-like ancestor with 12 chromosomes. a) Schematic representation of 13 segmental duplications within the rice genome (involving together > 5 Mb). Each block among the rice chromosomes Os01 – O12 represents duplicated regions containing colinear gene pairs as highlighted by identical colors. Three adjacent, but inverted, segmental duplications between Os10 and Os03 are summarized in grey. Chromosomes were arranged according to their duplication pattern into five groups. Recent rice-specific gene conversion among the first few Mb of Os11 and Os12 are indicted by arrows . b) Schematic representation of the structural model of the 7 barley chromosomes Hv1H – Hv7H that can be assembled by the repertoire of 12 rice-like ancestral chromosomes A01 – A12, which were named after the rice chromosomes. Barley Hv3H and Hv6H corresponded to the ancestral type of Os01 and Os02, respectively. The remaining barley chromosomes originated by combining two ancestral rice chromosomes (centromeres are indicated by black dots). Orthologous gene pairs provided evidence for the location of AD's (AD_1 to AD_7, see Figure 3 and Table S4 of Additional file 1). Two hypothetical additional AD's (AD_i and AD_ii) were confirmed by less than 8 orthologous gene pairs to one of the duplicated rice regions. Circular arrows indicate inversions. Asterisk symbols indicate cases, for which the orientation of ancestral chromosomes could not be identified in low-recombining central parts of barley chromosomes. After the divergence from rice, translocation of the distal segment corresponding to A03 from Hv4HS to Hv5HL took place in the Triticeae .