Abstract: Objective To observe and analyze the characteristic of mutation at STR locus. Methods 27 mutant genes observed in 1 211 paternity testing cases were checked by PAGE-silver stained and PowerPlex 16 System Kit and validated by sequencing. Results Mutant genes locate on 15 loci. The pattern of mutation was accord with stepwise mutation model. The mutation ratio of male-to-female was 8∶1 and correlated to the age of father. Conclusion Mutation rate is correlated to the geometric mean of the number of homogeneous repeats of locus. The higher the mean, the higher the mutation rate. These loci are not so appropriate for use in paternity testing.

Key words: short tandem repeat, mutation, sequencing, replication slippage