In forensics studies it is sometimes important to know the tissue of origin that
ID: 43419 • Letter: I
Question
In forensics studies it is sometimes important to know the tissue of origin that a DNA sample has come from. It turns out that different tissues have different methylation patterns for certain genes. Suppose there was a gene that showed a characteristic methylation pattern in sperm cells that was very different from that of blood or other tissues. Which experimental procedures would you use to analyze a tiny amount of DNA in a forensic sample to determine if that DNA had to come from sperm? Would you use PCR, bisulfite treatment; and in what order? Please explain your answer.
Explanation / Answer
The DNA varies from individual to individual. Each individual posesses a specific sequence called short tandem repeat (STR) or variable number tandem repeat (VNTR). These sequence are unique to every individual and do not match with other's DNA. Certain genes exhibit specific methylation patterns and these are characteristic only for those cells. Suppose the semen containing sperm cells id DNA evidence obtaines at a crime scene, then it is analysed by using PCR (polymerase chain reaction).
First the specific methylated sequences are identified and then appropriately matching primers are added to upstream and downstream sequences and the unique methylated sequences are amplified to get several copies and are analysed with DNA data bank samples for the matching of methylated sequences and to identify the victim.
The PCR is given the first priority in such type cases. At the latest several highly throuput sequencing technologies and updated processes like quantitative PCR and Realtime PCR can be employed. The bisulfite method is used in conditions where PCR is not available.