中文摘要：

目的检验来自不同地理位置和宿主,且归属于不同基因型的刚地弓形虫的GRA24基因的序列变异情况,评价GRA24基因能否作为研究弓形虫种群遗传学的理想标记。方法对所检刚地弓形虫的GRA24基因进行了序列比对,并使用了最大简约法,最大似然法以及贝叶斯法对所检验的虫株进行了系统进化分析。结果所检的虫株GRA24基因的有两种长度：6 240bp和6 264bp。所检GRA24基因的A＋T含量为40.82%~53.52%。序列比对显示有173个核酸变异位点（0.05%~0.2%）,其中有133变异位点个在9个内含子上,40个变异位点在8个外显子上;使用的3种方法构建的GRA24基因系统进化树的结果一致,GRA24基因不能将3种典型基因型的弓形虫虫株区分开。结论 GRA24基因的序列变异率较低,所以GRA24基因并不是一个研究弓形虫种群遗传学的理想标记。

英文摘要：

Among all phylum apicomplexa parasites,Toxoplasma gondii is one of the most successful parasites with a wide range of host,including human.As a newfound virulence factor,GRA24 is secreted into the parasitophorous vacuole（PV）.In the present study,we examined sequence variations in GRA24 gene among nine T.gondiiisolates from different hosts and geographical locations by PCR amplification,DNA sequencing and sequence analysis.The results have shown that two kinds of length of the GRA24 gene among all the examined T.gondii strains：6 240 bp and 6 264 bp.The A＋T contents were 40.82%to 53.52% among nine examined T.gondii strains.Results of sequence alignment shown that of all nine GRA24 gene sequences identified 173 variable nucleotide positions（0.05%-0.2%）,among those variable nucleotide positions,there were 13 transversions,27transitions in the coding regions,while a total of 133 variable positions were distributed in the 9introns regions among the examined T.gondii isolates,including 24 deletions,36transversions,73 transitions.The results of phylogenetic analyses using maximum parsimony（MP）,Bayesian inference（BI）and maximum likelihood（ML）based on the GRA24 sequences shown that the three Type II strains were not grouped together,suggesting that GRA24 gene sequence was not a suitable marker for phylogenetic and population genetic studies of T.gondii,but it may represent a potential vaccine candidate against toxoplasmosis.