Models of chromosome expansion based on the comparative microarray analyses and sequencing of chromosome-specific DNA clones presented here. Note that we make the assumption that all gene families are positioned at the same location in both Tb927-chrIa and Tb427-chrIb, and therefore that arrays expand/contract in situ. (A) Comparison of chrI size as estimated by PFGE analysis of different isolates of T. brucei (gray bars) with the theoretical maximum length estimated from the microarray and Southern blot analyses comparing the test chromosomes with Tb927-chrIa. Colored regions correspond to tandemly repeated genes and gene families that show a significant degree of polymorphism compared with Tb927. (B) Our proposed model of Tb427-chrIb organization. The central core is highly conserved compared with the sequenced Tb927-chrIa; sequences in the left subtelomeric region are amplified about twofold, but there is no VSG-ES. Results presented here indicate that the remainder of the additional DNA in Tb427-chrIb consists primarily of VSG arrays and associated sequences. We propose that this forms a hemizygous “subtelomeric” region of ∼2 Mb, and that this is probably on the right end of the chromosome.
