Objective To study the genetic polymorphism and frequencies of 15 STR loci in 10071 unrelated individuals of Han nationality, which are compared with the data reported previously. Methods 15 STR loci were amplified in DNA samples from 10071 unrelated individuals in Guangdong Han population using PowerPlex~(TM) 16 system, which were genotyped with ABI 377 or 3100 Genetic Analyzer. Frequencies for 15 STR loci were obtained. Results Except D8S1179 locus, rare alleles were found in the other 14 STR loci. The number of rare alleles ranged froml to 7 in the 14 STR loci ,which increased up to 34 rare alleles, including D21 S11 (32.1 and 36.2), D18S51 (15.2 and 17.2), Penta E (15.2, 17.4, 18.4, 19.4, 26 and 27), D7S820 (9.2, 10.1, 11.1 and 15), Penta D (18, 19 and 20), TPOX (14) and FGA (13) which were detected the first time and D21S11 (30.3), D7S820(9.1 and 9.2) which were frequently seen in the population although infrequent in European population. Conclusion More rare alleles can be detected with genetic polymorphism data from a lager number of individuals and more credible frequencies of alleles be obtained.

Objective To discuss the probability of siblings identification by autosomal short tandem repeat (STR). Methods 150 pairs of full siblings and 150 pairs of unrelated individuals were genotyped by the 15 STR loci of Power Plex?6 system. Paternity index of full siblings (Pips) and paternity probability of full siblings (WFS) were calculated with the method of ITO. WFS and allelic matching of the two groups were compared, and three sorts of allelic matching in each pair were tested by chi-square test. Results Wps of 100 pairs of siblings (66.67%) were more than 0.9995; WFS of unrelated individuals were less than 0.8, and that of 100 pairs (66.67%) were less than 0.27. The locus number of the entire-same ranged from 1 to 10, averaged 5.49 in siblings, while in unrelated individuals ranged from 0 to 5 and averaged 1.33; that of the entire-different ranged from 0 to 6, averaged 1.66 in siblings but ranged from 2 to 11 and averaged 6.57 in unrelated individuals; that of the half-same ranged from 3 to 13, averaged 7.85 in siblings, and ranged from 1 to 13, averaged 7.11 in unrelated individuals. By chi-square test, there was significant difference (P0.05) in the half-same between the two groups. Conclusion It is effective to identify siblings by Power-Plex?6 system. Testing of 15 STR loci of PowerPlex?6 system, it suggested that the pair were unrelated individuals when the locus number of the entirely-different is not less than 6 or that of the entirely-same is zero, and that the pair were siblings when the locus number of entirely-different is not more than 1 or that of the entirely-same is not less than 6.