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Quantitation of DNA is a method used to determine the quanity, or amount, of male and female DNA present in a sample. Quantitation using PCR (polymerase chain reactions) has shown to be extremely sensitive in detecting human specific DNA quantities and inhibitors. (Ginart et al. 2016) This test can detect DNA to the picogram level and provides forensic scientists with data to determine further action.
The results obtained during quantitation determine if a sample needs to be re-extracted, purified, or if there is a detectable presence of male DNA in the sample. Similar to the variability previously described with extraction protocols, there is variability in terms of what quantity, or female autosomal DNA to male DNA ratio, serves as the cutoff in order to send a sample forward for more testing. Quantitation, however, is still deemed a relatively fast method to determine if a sample is suitable for further DNA testing or if there is insufficient evidence to carry on the testing process.
If there isn’t enough male DNA detected, the sample from the sexual assault kit is commonly stopped here at the quantitation step. In terms of analyzing feminine sanitary products, obtaining a detectable amount of male DNA depends on the cutting that was taken from the product. As previously mentioned, the SAP-free upper layer may not contain as much male DNA as the lower core but it is commonly viewed as a more time efficient approach due to the challenges faced with the lower core.
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Generating a Profile
Currently for prosecution of the perpetrator of a sexual assault crime, the results of DNA testing and analysis must lead to the generation of individual profiles from the suspect and the victim (Voorhees et al. 2006). To establish a DNA profile from a sample, the sample must be sent forward from the quantitation phase of testing. Not all samples need to be amplified, but if one needs to be amplified it will be done before moving to the Genetic Analyzer and genotyping. A technique using Y-chromosome specific DNA is one way that forensic scientists can use to establish a profile (Sibille et al. 2002). This is done when a microscopic examination for the presence of spermatozoa was performed and a negative result was obtained.
The absence of spermatozoa is not indicative of the absence of male DNA. A negative microscopic examine may not show any spermatozoa due to the low concentration of sperm produced naturally by the male (oligospermic), the male being vasectomized, penetration by the male without ejaculation, and digital penetration. Conversely, autosomal STR analysis is preferred when the microscopic examination for spermatozoa is positive. This is because most of the Y-chromosome found in males doesn’t change with each new generation which brings into account the likelihood of paternal lineages during Y-STR analysis. Prior DNA analysis and methods of extraction are vital in order to establish an identifiable profile. When extracting DNA from a sanitary product, generating a DNA profile becomes more a challenge due to the previously mentioned SAPs.
Efforts to Detect Male DNA from Sanitary Products
Unfortunately among forensic laboratories, there isn’t a well-established protocol for quantitating male DNA from sanitary products. This is due to the challenge posed by superabsorbent polymers commonly found in the core of such products. When presented with SAP-containing products, forensic scientists, dependent upon methods implemented by their laboratory, may choose to not use the ‘y-screen’ approach of examination and instead perform a traditional serology screening of the evidence.
This screening process incorporates the use of alternative light sources which can cause semen to fluoresce indicating the location of the bodily fluid, a color changing test that reacts with seminal fluids, and another test that confirms the presence of the p30 protein which can be found in seminal fluids as well. While these methods of examination don’t depict the quantity of male DNA present in the evidence sample, they do however allow the scientist to determine if the bodily fluid in present. The most common traditional screening methods for sexual assault kits include the detection of acid phosphatase (using a presumptive color changing test) and the use of a confirmatory test that detects the presence of prostate specific antigen, or the p30 protein (Scott et al. 2019). Overall, these serology tests provide a qualitative rather than a quantitative result for the presence of male DNA.
Non-Procedural Challenges Faced by Scientists
Forensic scientists strongly encourage the collection of a sexual assault kit as soon as possible following a sexual assault. A delay in having a kit collected allows for the degradation of critical biological DNA and fluids. Often times, victims wait to have a kit collected due to a plethora of reasons including discussing the event with family or friends, the desire to shower, taking time to comprehend the recent event, and more. Additionally, a study conducted by Cerdas et al. (2016) investigated the whether a women experiencing her routine menstrual cycle affected the probability of finding male DNA in vaginal swabs from sexual assault victims.
The idea that a menstrual flow may increase the rate in which male DNA is expelled from the vaginal orifice, thus decreasing the probability of detecting male DNA, is one that is not unusual. However, Cedras et al. (2016) demonstrated that a woman experiencing her menstrual cycle (and the phase of the cycle) during the time in which a sexual assault occurs does not affect the amount of male DNA that can be recovered. Seeing as the probability of recovering male DNA is not impacted, the likelihood of generating a DNA profile is not affected either.
Conclusion
In conclusion, current research is being done to improve DNA extraction from feminine sanitary products but there isn’t a well-established method yet. Evidence containing superabsorbent polymers is common in forensic laboratories can pose a challenge to scientists. Gregório et al. (2019) discussed the practice of completely saturating the SAP so that the free-water immersing the sanitary product exceeds the absorbance capacity of the hydrogel, thus promoting the release of biological material.
The establishment of a set protocol for the separation of male and female DNA pertaining to sexual assault kits may decrease the variability between laboratories in the quantity extracted. Vuichard et al. (2011) propose that the initial lysis of the samples may have a large impact on the amount of male DNA that is recovered and ultimately extracted. Perhaps developing a well-established list of reagents that are the most useful for the extraction during sexual assault kits would allow for less variability among laboratories.
I believe this would be the start of a solution for the issue of variability of DNA quantities extracted because being able to generate a male DNA profile from samples in a sexual assault kit shouldn’t depend on the laboratory in which the kit is examined due to the variation in protocols the laboratory uses. This being said, there would also have to be an established set of protocols for extraction of feminine sanitary products seeing as the separation of the male component from the female can be more of a challenge than that of a typical swab.
