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Objective To explore the regularity of time-dependent changes in morphology and biomechanical properties of brain tissues in pigs, and value the feasibility of deducing the postmortem interval (PMI). Methods Brain tissues were taken from 42 pigs and kept in an artificial climate chamber with the temperature of 25 ℃ and humidity of 75%. The samples were collected from telencephalon at sequential time intervals (0, 12, 24, 36, 48, 60 h；n=6) according to the principle of predefined time, position, direction, ratio, quantity and shape. The samples fixed with formaldehyde were then immediately tested by mechanical testing machine to obtain their biomechanical parameters and the histological sections were prepared. Results With the extension of PMI (0-60 h), brain tissues gradually became discolored, weak, mudding and liquefied under the influence of autolysis and putrefaction. Both clearance area of the white matter and its integrated optical density (IOD) significantly increased during 0-48 h. Biomechanical properties of brain tissues including the limit load, average force, elastic modulus and fracture energy all presented a declining tendency at the interval of 12-60 h. The limit load was considered highly statistically significant, and statistical differences were found in average force, elastic modulus and fracture energy. Conclusions There exists a significantly negative structure-activity relationship between the morphology of brain tissues and biomechanical properties. The limit load of postmortem brain tissues in 60 h is the optimum in the window period, which can be used as a new method for estimating PMI.
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<p><b>OBJECTIVE</b>To study genetic polymorphisms of 20 Y-chromosomal short tandem repeats (STR) in Chaoshan Han population, and to evaluate their value in forensic science.</p><p><b>METHODS</b>Twenty Y-specific STR loci (DYS434, Y-GATA-A10, Y-GATA-H4, DYS438, DYS439, DYS443, DYS444, DYS446, DYS447, DYS448, DYS456, DYS458, DYS460, DYS520, DYS531, DYS557, DYS622, DYS630, DYS635 and DYS709) were amplified by using three fluorescence-labeled multiplex PCR systems and were analyzed by ABI310 genetic analyzer. One hundred and fifty-eight unrelated male individuals of Han population in Chaoshan area were investigated to determine the distribution of allele frequencies and haplotype.</p><p><b>RESULTS</b>The Y-STR multiplexes developed had followed the published nomenclature and ISFG guidelines for STR analysis. Gene diversity ranged from 0.2506 at DYS434 to 0.8034 at DYS447. A total of 157 different haplotypes were observed, and among these, 156 were unique, while 1 was found for two times. The haplotype diversity value calculated from all 20 loci combined was 0.999998. None of Y-STR allele mutation was observed in the 30 father/ son pairs confirmed by autosomal STR analysis.</p><p><b>CONCLUSION</b>The results indicate that the 20 Y-STR loci are highly polymorphic and fathership genealogy inheritance are stable. The three fluorescence-labeled multiplex amplification systems that we constructed are suitable for forensic individual identification and paternity testing in Chaoshan area.</p>