Overview of DNA Methods for the Identification and Individualization of Marijuana

Identifying a plant sample as Cannabis sativa is the first step in determining whether an illegal substance has been seized. Although three forms of DNA are present in plant cells (mitochondrial, chloroplast, and nuclear), nuclear DNA sequences are most commonly used for plant species identification. DNA-based tests for the identification of marijuana include the molecular analysis of the ITS1, ITS2, and trnl intron. A comparison of the ITS1 and ITS2 polymerase chain reaction (PRC) product sizes in five samples of marijuana and in one sample of a close relative revealed a size difference between marijuana and Humulus for the ITS2 region. Other tests using PCR amplification and subsequent restriction enzyme digestion of the tml region of the chloroplast has shown that marijuana DNA profiles can be generated and compared between samples, making DNA tests useful for forensic purposes. After a forensic sample has been identified and classified, it is important to individualize the samples. This involves establishing linkage between the evidentiary sample and the source. There are several ways that plant samples can be tested by using DNA-based methodologies in forensics. These include randomly amplified polymorphic DNA (RAPDs), amplified fragment length polymorphisms (AFLPs), and short tandem repeats (STRs). Each of these methods is described in detail. In order to give significance to the meaning of a random match, comparative databases must be constructed. When constructing such databases, it is important to consider the sampling strategy and the final purpose of the database. Nationwide and Connecticut State marijuana databases are under construction and may be used for both establishing the extent of genetic diversity within and between seizure samples and for estimating the expected frequency of a random DNA match. 2 tables, 3 figures, and 65 references