The likelihood of any two individuals having identical STR profiles is less than one in a quintillion (1,000,000,000,000,000,000).ĭNA profiles can be entered into a database called Combined DNA Index System (CODIS) so that federal, state, and local agencies can exchange and compare DNA profiles electronically. But if the two samples match across all 20 STRs (Suspect 3), a statistical calculation would be made to determine the frequency at which the full set of STRs is observed in the population. If the STR profiles from the two samples do not match, the individual would be excluded as the source of the crime scene evidence (Suspects 1 and 2). The profile from the sample from the crime scene is compared to the sample from the suspect (similar to the image to the right). In the United States, law enforcement agencies and the Federal Bureau of Investigation (FBI) analyze 20 STRs when creating DNA fingerprints. Afterwards, the STRs are separated according to their size. The region containing each STR being analyzed is then copied many times using a technique called polymerase chain reaction. To create a DNA fingerprint, DNA must first be extracted from a sample collected from a crime scene, a suspect, or an individual in a paternity case for example. The differences in the number of repeats means that people have STRs of different lengths which can easily be measured using a few lab techniques. For example, I might have a CAG unit that is repeated five times while you have CAG repeating eight times. There are many STRs throughout the genome, each having different repeating units with different numbers of repeats.Įveryone has the same STR at the same place in the genome but the number of repeats varies between individuals. STRs consist of a string of repeating DNA nucleotides that are usually two to five bases long (like CAGCAGCAG or AATGAATGAATG for example). Originating in the mid-1980s, DNA fingerprinting is now commonly used as a law enforcement tool.ĭNA fingerprinting looks at differences in sections of DNA called short tandem repeats (STR). A technique called DNA fingerprinting takes advantage of some of these differences to identify individuals based upon their DNA. However, determining the likelihood of a DNA match between a suspect and a crime scene is a complicated process.Īlthough 99.9% of genomes are identical across all humans, there are regions of variation that are unique to each individual. Finding a perpetrator and bringing them to justice using DNA is often portrayed as a simple, exact, and infallible method. If you’re a true crime fan like me, you have probably seen your fair share of investigations on popular television shows. Skin cells, blood, hair follicles, and saliva all contain DNA that can be used to identify an individual. DNA can also be used to define paternity, exonerate the wrongly accused, and identify victims of crime, disasters, and war. Because we each have a unique DNA code, it can also be used to identify individuals.įorensic science increasingly relies on small bits of DNA left at crime scenes to link criminals to the crimes they commit. Our cells use the DNA code to make the proteins and molecules necessary for all of the functions of our body. It is made up of four nucleotide bases, represented by the letters A, T, C and G. There is DNA in nearly all of the cells of our body. Let’s learn about how DNA and genetics play a role in solving cases. Advances in DNA sequencing technology over the past few decades, however, has led to a surge in both convictions and exonerations for many crimes. For me, though, I am most intrigued by the science behind the true crime curtain.įorensic science, or the use of scientific methods to investigate crimes, has helped solve cases in the criminal justice system for centuries. I even followed the breaking of the Golden State Killer case with bated breath. I binged the documentary shows The Jinx and Making a Murderer. And I will admit, as a 30 something year-old who grew up watching shows like CSI and Criminal Minds, I got caught up in the true crime wave.Įvery week I listen to My Favorite Murder and The Murder Squad podcasts. Hundreds of true crime podcasts and documentaries are available in our streaming feeds. The true crime genre really boomed over the past few years.
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