A previously validated, 13-autosomal STR multiplex was used to genotype 510 samples of marijuana from four different sites, i.e., 21 seizures at the US-Mexico border, Northeastern Brazil, hemp seeds purchased in the U.S., and the Araucania area of Chile; and a reported multi-loci system was modified and optimized to genotype five chloroplast and two mitochondrial markers.
Since Cannabis sativa (marijuana) is a controlled substance in many parts of the world, the ability to track the biogeographical origin of cannabis could provide law enforcement with investigative leads regarding its trade and distribution. Population substructure and inbreeding may cause cannabis plants to become more genetically related. This genetic relatedness can be helpful for intelligence purposes. Analysis of autosomal, chloroplast, and mitochondrial DNA allows for not only prediction of biogeographical origin of a plant but also discrimination between individual plants. The current study designed two methods: a homopolymeric STR pentaplex and a SNP triplex with one chloroplast (Cscp001) marker shared by both methods for quality control. For successful mitochondrial and chloroplast typing, a novel real-time PCR quantitation method was developed and validated to accurately estimate the quantity of the chloroplast DNA (cpDNA), using a synthetic DNA standard. A sequenced allelic ladder was also designed for accurate genotyping of the homopolymeric STR pentaplex. For autosomal typing, 356 unique profiles were generated from the 425 samples that yielded full STR profiles and 25 identical genotypes within seizures. Phylogenetic analysis and case-to-case pairwise comparisons of 21 seizures at the US-Mexico border, using the Fixation Index (F ST ) as genetic distance, revealed the genetic association of nine seizures that formed a reference population. For mitochondrial and chloroplast typing, subsampling was performed, and 134 samples were genotyped. Complete haplotypes (STRs and SNPs) were observed for 127 samples. As expected, extensive haplotype sharing was observed; five distinguishable haplotypes were detected. In the reference population, the same haplotype was observed 39 times and two unique haplotypes were also detected. Haplotype sharing was observed between the US border seizures, Brazil, and Chile, and the hemp samples generated a distinct haplotype. Phylogenetic analysis of the four populations was performed, and results revealed that both autosomal and lineage markers could discern population substructure. (publisher abstract modified)
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