三个短串联重复序列位点的等位基因遗传变异研究

目的 探讨短串联重复序列（short tandem repeats,STRs）遗传变异的方式及机理。方法 用银染方法对3个STR位点（FGA、D12S391、D11S554)共19个发生突变的家系父、母、子的DNA样本进行SRT基因分型，将需测序的等位基因条带从凝胶上切下，再进行PCR扩增，产物经纯化作为测序模板，采用循环测序法测序。结果 19个家系中有18个家系子代新产生的等位基因变异表现为一个重复单位的增加或减少（表现为一个重复单位增加的有8个家系，减少的有7个家系，不确定的有3个家系），只有1个家系表现为2个重复单位的减少，子代新产生的等位基因来自父亲的有13个家系，来自母亲的有3个家系，不能确定的有3个家系，来自父与母的比较约为4：1。3个STR位点等位基因突变都出现在长的、连续的四核苷酸重复区（FGA的“CTTT”区、D12S391的“AGAT”区、D11S554的“AAAG”区）。结论 FGA、D12S391和D11S5543个STR位点的等位基因突变主要表现为一个重复单位的增加或减少占95％，其次是两个重复单位的变化，没有碱基的插入或缺失，突变主要来自父亲，在这3个STR位点中的长的、连续的四核苷酸重复区可能是等位基因突变的敏感点。

Study on the mutation of human short tandem repeats at three loci

OBJECTIVE: To understand the mutational patterns and mechanism of short tandem repeats(STRs). METHODS: The DNA samples of 19 parent-child pairs with mutations in three loci (FGA, D12S391, and D11S554) were genotyped by silver staining on STR. Alleles to be sequenced were excised from gels, reamplified by PCR, and purified. Sequencing was performed by use of cycle sequencing. RESULTS: There were 18 out of 19 pedigrees in which the 'new' alleles gained or lost a single repeat (8 gains, 7 losses, and 3 being indistinguishable). Only one pedigree lost two repeats. In the 19 pedigrees, there were 13 pedigrees whose 'new' alleles came from fathers, 3 from mothers, 3 from either father or mother. The ratio was 4 1 between fathers and mothers. The mutation of three STR loci occurred in the long, uninterrupted tetranucleotide repeat regions ('CTTT' in FGA, 'AGAT' in D12S391, and 'AAAG' in D11S554). CONCLUSION: Single- step mutations accounted for 95% of STR mutation events in these three loci: FGA, D12S391, and D11S554. The rest were double step mutations.There was no insertion or deletion of an incomplete repeat in any of the pedigrees. The mutation was mainly caused by fathers. The long, uninterrupted tetranucleotide repeats in these three loci might be susceptible to mutation.