Abstract: Objective To explore the change rules of peak area ratio of STR loci to Amelogenin （AMEL） locus （STR/AMEL）, a sex-determining gene in DNA degradation, and to evaluate the application of STR/AMEL value in the estimation of DNA degradation degree. Methods DNA was extracted from iliopsoas, and the variations of STR/AMEL value （Penta E/AMEL, Penta D/AMEL, FGA/AMEL） were analyzed after the artificial degradation was made by DNaseⅠ, and the changes of these three ratios of the iliopsoas naturally degraded in an outdoor environment were also analyzed. The regression curves were analyzed using the periods of DNA degradation and outside the body as the independent variable （x） and the STR/AMEL value as the dependent variable （y） and three curve equations under two conditions were established. Results Both under the conditions of artificial and natural degradation, STR/AMEL value had a negative relationship with the degradation time. The relationship between STR/AMEL and degradation time can be well simulated by the cubic function. R2 was over 0.99 under controlled degradation condition and over 0.86 under natural degradation condition. Conclusion The STR/AMEL value （Penta E/AMEL, Penta D/AMEL, FGA/AMEL） is negatively related with the DNA degradation degree, which follows mathematical regression models strictly, and it might be applied to evaluate the DNA degradation degree.

Key words: forensic genetics, DNA degradation, necrotic, short tandem repeat, peak area