The human genome is particularly rich in low-copy repeats (LCRs) or segmental duplications (5%-10%), and this characteristic likely distinguishes us from lower mammals such as rodents. How and why the complex human genome architecture consisting of multiple LCRs has evolved remains an open question. Using molecular and computational analyses of human and primate genomic regions, we analyzed the structure and evolution of LCRs that resulted in complex architectural features of the human genome in proximal 17p. We found that multiple LCRs of different origins are situated adjacent to one another, whereas each LCR changed at different time points between >25 to 3-7 million years ago (Mya) during primate evolution. Evolutionary studies in primates suggested communication between the LCRs by gene conversion. The DNA transposable element MER1-Charlie3 and retroviral ERVL elements were identified at the breakpoint of the t(4;19) chromosome translocation in Gorilla gorilla, suggesting a potential role for transpositions in evolution of the primate genome. Thus, a series of consecutive segmental duplication events during primate evolution resulted in complex genome architecture in proximal 17p. Some of the more recent events led to the formation of novel genes that in human are expressed primarily in the brain. Our observations support the contention that serial segmental duplication events might have orchestrated primate evolution by the generation of novel fusion/fission genes as well as potentially by genomic inversions associated with decreased recombination rates facilitating gene divergence. The genome architecture resulting from the size, orientation, and arrangement of LCRs was shown to be responsible for genomic instability (Lupski 1998;Emanuel and Shaikh 2001;Stankiewicz and Lupski 2002a). Serving as substrates for nonallelic (or "ectopic") homologous recombination (NAHR), LCRs facilitate meiotic and potentially mitotic DNA rearrangements associated with several diseases that are referred to as genomic disorders. Genomic rearrangements can be responsible for Mendelian traits, contiguous gene syndromes, and whole-arm chromosome aberrations (Lupski 1998Stankiewicz and Lupski 2002a). During the last decade, substantial molecular data have emerged documenting that LCR-mediated NAHR is a major mechanism for human disease (Emanuel and Shaikh 2001;Stankiewicz and Lupski 2002a;Shaw and Lupski 2004).Several studies have shown that LCRs arose recently, apparently during primate evolution (Stankiewicz and Lupski 2002b). Recent data suggest that LCR-associated genome architecture does not represent simple segmental duplications but rather reflects complex rearrangements that are potentially the end product of multiple events (van Geel et al. 2002). These serial segmental duplications can result in a complex shuffling of genomic sequences (Babcock et al. 2003;.The gene-and LCR-rich human genomic region 17p11.2-p12 is rearranged in a variety of different constitutional, evolutionary, and cancer-associated structural chromoso...

Recognition of variation patterns at the level of DNA, chromosomes and plant morphology, and their interrelationships were the object of this research on Brachypodium distachyon. RAPD profiles, cytogenetics of root mitoses, gross morphology and microstructures were studied in B. distachyon for 18 accessions, as well as for three selections with a narrowed gene pool, all from the Mediterranean and Irano-Turanian region. For the scored RAPD bands, 309 were polymorphic (96%). The average expected gene diversity (H i ) for all primers was 0.220, which is close to the variation noted in the Asian-European region of origin. In the UPGMA dendrogram, accessions were not clustered according to their geographic origin. High variability in cytogenetics was found. Levels of chromosome ploidy differentiated accessions. A cytogenetic mosaic was expressed in the form of aneuploidy and anomalous mitoses. Accessions presenting similar cytogenetic variability were not clustered in the RAPD dendrogram. The period of vegetative growth varied greatly. Zoochoric characteristics of diaspores and endosperm volume showed interaccessional variability. No distinct linkage between RAPD patterns and morphology was found. High variation in all studied characteristics of the plant was noted, which is a good base for natural selection of intraspecific units (inbred lines). The narrowing of the gene pool is an effective tool of microevolution and facilitates the distribution of the species according to the founder principle. The comparison of this evolutionary potential of B. distachyon with patterns of evolution of other annual weedy grasses would be of great value for weed science.