Abstract: 　Objective] To investigate the intraspecies phylogeny and genetic diversity of G. lamblia . [Methods] Total genomic DNA was extracted and partial fragments of tim gene were amplified by PCR. All the nucleotide sequences were analyzed by means of phylogenetic analysis, which were constructed with pasimony and N J methods. [Results] A total of 124 variable sites (23% of the total sequences detected) were defined, most of which were found at the silent sites of codons. Two similar phylogenetic trees were constructed, subdividing 16 isolates into two groups. [Conclusion] The genetic diversity of G. lamblia appear to be little affected by both the host and geography, while natural selection might play an important role at the DNA molecular evolution level of tim gene. The tim gene may be considered to be a very useful genetic marker of the population genetic structure of G. lamblia .

Key words: Giardia lamblia, triose phosphates isomerase, sequence analysis, phylogeny, genetic marker.