Comparison of structure and numbers of genes among cereals
谷类作物基因结构及其数量的比较

This review describes the current state of knowledge regarding cereal genome structure. Annotation based on the sequencing of long genomic segments from cereals and the whole-genome analyses of Arabidopsis and rice,suggests that a mosaic structure consisting of recombinationally active gene-rich islands that are separated by blocks of high-copy DNA. Macrocolinearity within the cereals is conserved. By analysing the gene order of the Sh_2/A_1 orthologous region of maize, rice, sorghum, wheat, and barley, the Sh_2 and A_1 homologs are separated by 20 kb in rice and sorghum and by 140 kb in maize. The synteny in the Sh_2/A_1 region is interrupted by a break between the X_1 and X_2 genes in the triticeae. The colinear between A_1 and X_2 genes remains in homeologous chromosomes as in other grasses, but that between Sh_2 and X_1 orthologs were translocated to a nonhomeologous chromosome. Through three forms of duplication, i.e. polyploidization, segmental duplication, and local gene amplification, increases the number of paralogous gene sequences found in plants. At the level of individual genes, microcolinearity is frequently disrupted. Preliminary evidence from comparative analysis of sequenced orthologous genomic segments suggests that local gene amplification and translocation within a plant genome may be linked in some cases.