Suppose you grew up compulsively watching criminal investigation programs using face recognition app. In that case, you undoubtedly share the fascination with the idea that we can tie a person to a crime they committed by collecting their DNA from a little drop of blood they left behind. However, have you ever wondered how forensic experts could distinguish between individuals using their DNA? Continue reading to learn more, whether you’re considering a career as a forensic DNA analyzer or just interested in how it all works.
The Scientific Theory
For those who need a biology review, ancestry DNA testing is the genetic code found within each of our cells. It gives instructions on which proteins each cell should produce. The sequence in which the letters A, T, C, and G occur in this code determines what proteins are made, how many are produced, and how rapidly. DNA is packaged into bundles called chromosomes. We have two copies of each DNA sequence as a result.
Using What We Have Learned
Let’s apply everything we’ve learned to a fake sample case. Imagine that a masked intruder broke into Bill’s home and knifed him. Bill successfully repels the attacker, who flees while still carrying the knife. When the police show up there, they give over the blade to forensics, who can effectively extract the attacker’s DNA from the handle. David, a coworker of Bill’s who was just dismissed due to a complaint Bill had made against him, is the person Bill believes to be the attacker. To match David’s DNA to the DNA found on the knife handle, the police take a sample of David’s DNA along with that they also do paternity testing.
To everyone’s amazement, David’s DNA has two alleles, one with eight repeating GA units and the other with six teams! Even though it is evident that David despises Bill, we have shown that the DNA found on the knife handle did not originate from David.
Having unintentionally scratched Todd’s cherished Porsche, Bill then names Todd as a possible suspect. When the police take Todd’s DNA, they discover that it contains one allele with eight repeating units and another with seven teams at this microsatellite, much like the DNA from the knife handle. So now that Todd’s guilt has been established, he must go to prison, right?
It’s not difficult to conceive that we may discover thousands of people with identical alleles and repeat units at the same microsatellite, given that australian shepherd rat terrier mix big city may have up to one million persons. Because of this, we can only infer that David “may” have been the attacker, which is insufficient evidence to convict. How, then, can we be sure?
Assay Instruction Manual
A portion of a real-world STR profile is seen in the figure above. The microsatellites are divided on this figure (an electropherogram) based on their size (i.e., the total number of A, T, C, and G that make up the DNA sequence). The names of the microsatellite sites being monitored are represented by the coded strings of letters and numbers above. The narrow peaks represent the alleles of the two copies of that microsatellite under these names. The number beneath each mountain represents the quantity of repeating units at that copy. For instance, this person possesses two copies of a microsatellite, one with 12 repeating units and the other with 14, at the D5S818 locus. They have two documents at the D16S539 locus, one with ten repeating units and the other with 12 repeating units.
Quick DNA and Face Recognition App.
The microsatellite that Todd and the masked attacker shared, with 7- and 8-unit repetitions, may be seen at locus A on the electropherogram shown above. Further examination reveals that they still possess identical alleles at loci B, D, and E. On closer investigation, we see that Todd has ten and 15-unit repetitions at locus C, while the masked attacker has ten and 14-unit repeats. Additionally, Todd possesses ten and 14-unit repetitions at locus F compared to the masked attacker’s seven and 14-unit repeats.
Unfortunately, Todd’s DNA was not present on the knife handle despite being so near. It seems that we’ll need to start again and either identify fresh suspects or submit the profile of the masked attacker into CODIS to see if we can obtain a hit. A bit depressing, but such is a DNA analyst’s everyday routine. Further, the analyst can use modern technology like face recognition apps to find results from other aspects.
Conclusion
This article taught us how forensic DNA analyzers distinguish between individuals by comparing the amount of repeating units in each copy of the microsatellites located at various DNA loci and using modern technology like a face recognition app. We may instantly assume that we are looking at two distinct people if even one allele at one site differs. We must compare numerous loci because, even if all the alleles match, we cannot be assured that it is the same individual. The probability that two persons will be found to have identical alleles at every site decreases as the number of loci we compare increases.
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