Repetitive sequences: cause for variation in genome size and chromosome morphology in the genus Oryza.

摘要

Large variations in genome size, as determined by nuclear DNA content and mitotic chromosome size, were identified in 11 diploid Oryza sp. using flow cytometry and image analyses. Total chromosomal length (r = 0.939) and area (r = 0.927) were highlycorrelated with nuclear DNA content. Among the species examined, O. australiensis (E genome) and O. brachyantha (F genome) had the largest and smallest genomes, respectively, whilst O. sativa (A genome) had an intermediate genome size. Distribution patterns of genome-specific repetitive DNA sequences were physically determined using fluorescence in situ hybridization. O. brachyantha had limited sites of repetitive DNA sequences specific to the F genome. O. australiensis showed overall amplification ofgenome-specific DNA sequences throughout the chromosomes. It is concluded that the total number of repetitive DNA sequences contribute, whether they are genome-specific or not, to the nuclear DNA content of each species. Selective amplification of genome-specific sequences therefore causes genome differentiation in reference to both genome/chromosome size and chromosome morphology in diploid rice species.