Semen DNA Analysis:This process involves identifying and examining DNA within a semen sample. Suppose there's an allegation that a man's semen is present on a piece of fabric. To determine if the suspected individual's semen has stained the cloth, DNA testing can be conducted. Here's the procedure:Initially, it's necessary to confirm that the stain is indeed semen. Under ultraviolet light, semen fluoresces and also reacts by changing color when exposed to certain chemicals. If these preliminary tests are positive, lab technicians will cut out a section of the fabric where the stain is located. This piece is then immersed in a special solution to dissolve the organic material within the stain. Technicians then search for cells in the solution using a basic low-power microscope. Sperm appear as small, inactive tadpoles. If sperm are visible, the next step is extracting DNA from them. This involves using a mild detergent to break open non-sperm cells, followed by a water rinse to remove these broken cells. A stronger detergent is then used to burst the sperm cells and retrieve their DNA. The DNA extracted from the semen is compared to the suspect's DNA, obtained from a blood or other sample. In cases where the stain is small and contains little DNA, the polymerase chain reaction (PCR) method is applied to amplify specific DNA segments. PCR increases the quantity without altering the DNA itself. The DNA from the semen is then compared to the suspect’s DNA using a technique known as restriction fragment length polymorphisms (RFLPs). To analyze RFLPs, special enzymes cut the DNA into fragments. Different DNAs are cut differently by these enzymes. If both the suspect's and the semen sample's DNA are cut into the same number and length of fragments, the semen could belong to the suspect. The probability that the semen's DNA belongs to the suspect is then calculated. For instance, the likelihood might be one in 11 million that the DNA originated from someone other than the suspect.Depending on the methods and laboratory conducting the tests, DNA analysis of semen can take several days to weeks for results. The tests might reveal that the semen does not belong to the suspect, or they might show no distinguishable difference between the suspect's DNA and the semen's DNA. However, DNA testing cannot definitively prove that the semen is from the suspect.
