Each individual has their own unique genetic fingerprint and
in the instance a crime has occurred, this genetic fingerprint can be useful in
identifying perpetrators or even link victims to the original crime scene in an
instance that the body was moved. The journal article Methylation Markers for theIdentification of Body Fluids and Tissues from Forensic Trace Evidence poses
the question if there are specific methylation markers on DNA that can identify
with positivity what type of bodily fluid is present at a crime scene and if
exogenous or endogenous factors skew the methylation.
I found this research interesting because it was one of the first to actually take into account the exogenic and endogenic changes that body fluids come into contact with at a crime scene. The study's goals were to describe an epigenetic marker set using methylation on regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide (CpG sites) for venous blood, menstrual blood, vaginal fluid, saliva, and sperm. These body fluids were chosen specifically because they are the most prevalent at a crime scene. Their hypothesis stated that because many methylated loci are involved in cell-specific gene expression, quantifying the degree of methylation at these positions could identify a cell line with accuracy.
Within the research Forat et al. tested different variables that the body fluid could undergo at a crime scene and their effects on the methylation by first finding reciprocal marker loci. This means that they wanted to find loci for which the target body fluid was unmethylated while the remaining fluids' loci were methylated. After the markers were located, the body fluids were placed in sample environments: dry on room temperature, wet in an exsiccator, outside on the ground. Each sample was tested after 1, 2, 3, and 6 months.
I found this research interesting because it was one of the first to actually take into account the exogenic and endogenic changes that body fluids come into contact with at a crime scene. The study's goals were to describe an epigenetic marker set using methylation on regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide (CpG sites) for venous blood, menstrual blood, vaginal fluid, saliva, and sperm. These body fluids were chosen specifically because they are the most prevalent at a crime scene. Their hypothesis stated that because many methylated loci are involved in cell-specific gene expression, quantifying the degree of methylation at these positions could identify a cell line with accuracy.
Within the research Forat et al. tested different variables that the body fluid could undergo at a crime scene and their effects on the methylation by first finding reciprocal marker loci. This means that they wanted to find loci for which the target body fluid was unmethylated while the remaining fluids' loci were methylated. After the markers were located, the body fluids were placed in sample environments: dry on room temperature, wet in an exsiccator, outside on the ground. Each sample was tested after 1, 2, 3, and 6 months.
The discrimination power of these markers are very high
because in all cases there is at least 1 marker for each kind of fluid and
they show no overlap distribution of methylation rates compared to each fluid.
Thus showing that each of the body fluids can be positively identified using
the method explained in the article. The researchers even went on in explaining influences
that made the results less clear. A large example was that tumors have an
effect on the methylation patterns in women with cervix cancer.
This research is significant in the field of forensic science because it moves away from using RNA to identify body fluids since RNA is less stable in a variety of different conditions. Another surprising result was that each time a body fluid was examined, even when the body fluids were mixed, the method identified the fluids 100% of the time.
This research is significant in the field of forensic science because it moves away from using RNA to identify body fluids since RNA is less stable in a variety of different conditions. Another surprising result was that each time a body fluid was examined, even when the body fluids were mixed, the method identified the fluids 100% of the time.
Kari,
ReplyDeleteI think it's really cool that they have found a way to 100% identify fluids at a crime scene. This is a big advancement because like you said, RNA is so unstable. With the different environments tested, different lengths of time, and the fluids mixed, it was a well thought out experiment.
Since this research shows that they were able to identify the fluids 100% of the time, is this a common practice in the forensics field or is more research needed before it becomes a common practice? It sounds like this should be a technique that is commonly used to identify bodily fluids.
ReplyDeleteKelsey, I am not 100% positive. I found this article when I was in my undergraduate seminar class and I have talked about it here and there within my department. As I am just a baby MSFS student, I am interested in using methylation as a means of identification of body fluids. One of our professors is also doing research around this idea. I agree with your statement that this should be a technique used because it is so beneficial and accurate.
DeleteHoly crap. Illumina is a really incredible company. I was initially all like, how could they possibly tell in mixed fluid samples. Then I read about the bead chip. I repeat, holy crap: http://www.illumina.com/products/methylation_450_beadchip_kits.html
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