which medium do you like better and why?

is dna forensic analysis reliable? guilty as charged.

kathryn holmes, department of justice

what if you came home one day and discovered your ipod was not in its usual place? instead of resting on your nightstand, you found it tossed on the floor with a big scratch on the screen. first, you would examine the scene. picking the ipod up, you see it has a peanut butter smudge on it. that’s when you start making a mental list of potential ipod-scratching suspects. since you have a little brother and sister whose favorite afternoon snack is peanut butter crackers, you determine they are the prime suspects. but which one committed this offense? you storm down the stairs to begin your investigation.

when law enforcement is faced with a real crime and must analyze a crime scene, they take a much more detailed approach. using science and technology, they can conduct what is called a forensic analysis. for example, the police might find written documents and have the handwriting analyzed by an expert. they can even use ballistics testing to examine markings on a bullet to see if it was fired from a suspect’s weapon.

but out of all the methods, the most reliable forensic technique police use is called dna fingerprinting. as opposed to traditional fingerprinting in which the actual fingerprints are lifted from the crime scene, this type of fingerprinting looks inside the cell of a human being to determine who committed the crime.

scientists and investigators count on dna fingerprinting for its accuracy. that’s because dna is similar to a fingerprint—everybody’s dna is different. (the only exception is identical twins. they have the exact same dna.) this unique genetic code can be found in all body cells, including hair, skin, and blood. that means investigators can examine these types of evidence found at the scene of the crime, with the hopes of matching it to a suspect’s dna.

although it is widely used today, dna analysis technology has not always been around. scientists developed this method in the 1980s. since then, police and investigators have used it to convict criminals and solve numerous crimes. this technology has proven useful in solving cold cases, too. those are cases that were previously thought to be unsolvable.

but dna analysis isn’t just for convicting criminals. over the past few decades, it has been used to free prisoners who were wrongly convicted of a crime. some of these prisoners were even on death row. archeology is another profession that uses dna analysis. ancient peoples are studied using dna samples taken from 3,000-year-old mummies. the scientists determine interesting characteristics, such as the health of the egyptian family lineage. a more recent use of dna analysis involves preventing health problems before they start. if a person’s dna indicates that he or she has a propensity for heart problems, he or she could start exercising and eating well in order to avoid getting sick.

since the start of dna analysis, investigators needed a way to keep track of all the data they were collecting from crime scenes. so the fbi and the u. s. department of justice developed what’s called the “combined dna index system,” or “codis” for short. codis is a database of dna records of convicted offenders. it is used worldwide to share and compare dna data. any forensics laboratory can use codis for free to run a dna sample against the database to see if there are any matches. once a criminal’s dna code is in the system, it remains there for identification in future crimes.

although dna fingerprinting would not really be used to solve the mystery of the scratched ipod, for more serious matters, investigators around the world agree—when it comes to reliability, dna analysis is guilty as charged.