Figure 5

Hypothesis for the origin of AAT loci on chromosomes 4 and 8 in T. brucei. a. Three gene lineages were present on the ancestral chromosome; these were ancestral to the AAT3/AAT8 loci, the AAT4/AAT7 loci and the AAT1 locus respectively. b. Tandem duplication created a dimorphic locus, ancestral to the contemporary AAT4 and AAT7 loci. c. A transpositive duplication of one sequence type from AAT4/7 produced the monomorphic AAT2/10 locus on the same chromosome. d. A block duplication of the chromosome (denoted by dashed line) resulted in two paralogons (now attached to chromosome 4 and 8). This duplicated the ancestral gene lineages, creating the contemporary loci. Among AAT4 and AAT7 other events affected gene number and sequence: CE – concerted evolution, GC – gene conversion, RC – evolutionary rate change. AAT1 has no paralog on chromosome 8, and so must have been lost. e. AAT9 must have been transposed later since it has no paralog on chromosome 4, and is unrelated to the other loci.