MAPPING VARIATION IN CHROMOSOME HOMOLOGS OF DIFFERENT GIARDIA STRAINS

A landmark physical map of the 2-Mb chromosome of the Giardia duodenal is cloned line WB-1B, constructed using randomly cloned, chromosome sp ecific markers, was used to compare the organisation and map order of the equivalent chromosome in other strains. A representative marker fr om each of the 13 NotI segments of the 2-Mb chromosome was hybridized to NotI cleavages of whole chromosomes of the other strains. Two strai ns, one isolated from a human, and one from a cat, had the same chromo some hybridization patterns as WB-1B. A strain isolated from a sheep, had one NotI chromosome 5 segment larger than WB-1B. Two additional st rains isolated from a calf and a human had significantly different Not I cleavage patterns from the previous strains and shared no similar-si zed chromosome NotI segment from their 2Mb chromosome homologues and o nly one in common with WB-1B. In one strain, two markers from the same WB-1B NotI segment did not hybridize suggesting deletion events have occurred. The order of some NotI segments within the 2Mb chromosome ho mologue was maintained, as determined from partial NotI chromosome cle avages, while in the most divergent of strains internal chromosome rea rrangements and deletions were evident. All but one of the 2Mb WB-1B c hromosome markers examined hybridized to a single chromosome band in a ll strains. Thus, while Giardia chromosomes vary in size, copy number and organisation, some linkage of markers is apparently maintained in isolates from disparate hosts and localities. We have therefore genera ted a genetic analysis system for Giardia with landmark maps using rep resentative markers to replace the paucity of classical genetic marker s and mutants. This approach is being extended to the complete genome.