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Genetics in the Courtroom

By Caroline Zeng

Not only is our DNA present in every one of our cells, but it also present in the cells that we leave behind everywhere we go. In fact, we can be identified by flakes of our skin, strands of our hair, bits of blood and saliva, and more. The field of forensics science applies what we know about our genes and genetic sequencing, to the judicial system by identifying criminals and connecting them to the crimes they commit. But how does it work?

Forensics science relies heavily upon variations of the human genome particularly sequences known as short tandem repeats or STRs. An STR consists of repeated short (typically three- to four-nucleotide) DNA sequences (Norrgard, 2008), referred to as an allele. These are located at specific regions, or loci, in the genome, known as markers. Not only are these regions easily measured and compared among individuals, but because each person inherits two different chromosomes (maternal and paternal), the different number of repeats on each allele, further specify their DNA profile. The FBI have identified 13 loci that are widely used.

To determine this information, scientists first extract DNA from cells preferably from blood or other fluids, copy the DNA using polymerase chain reaction (PCR) and then separate these segments using gel electrophoresis. They then study an electropherogram which displays peaks with a specific number of repeats at each allele marker. The DNA profile of a person combines the number of repeats at a specific marker, and enters the numbers as pairs (for each loci) into a database. Currently, however, compelling all individuals to submit their genetic information into a database is a topic of debate.

The advances in the field of forensics science has broad implications. Some include, resolving paternity disputes and solving “cold cases.” In paternity cases, a DNA sample is obtained from both the child and the father in question. By comparing the relatedness of the repeats at specific markers, these cases are resolved both quickly and accurately. On the other hand, cold cases are cases that have never been fully solved but have been put aside for more pressing matters. It is probable that at the time, DNA profiling/sequencing was not available yet, but now new information can be brought to light. The new technology allows scientists to revisit old forensics evidence or even test individuals that they couldn’t before. This could either link suspects to the crime, or exonerate those that were wrongfully imprisoned/punished.

So while our DNA is incredibly helpful inside of our cells, new advances in the forensics field proves that our unique genetic sequences can be helpful in other environments, such as a courtroom.

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