If you’ve ever seen an episode of CSI or Law and Order, you know the term DNA fingerprinting. It’s is a term that has been thrown about on TV and in the press for around 20 years now, largely due to its definitive power to denounce the guilty and save the innocent, but how does it actually work, and what does it mean? The one sentence summary is that it’s a method to determine the probability that genetic material came from a specific individual. Over ninety nine percent of our DNA is is actually the same between individuals, but it’s that one percent that is different that enables scientists to distinguish each one of us from everyone else.
DNA fingerprinting basics
The DNA code is made up of four key building blocks – A, G, C and T, called bases, which are joined together in long chains to spell out the work horses of the genome: genes. These are the elements that instruct our cells on what to do and how to grow and function normally.
However the gigantic mass of DNA we have doesn’t all code for essential functions. In fact large amounts of sequence is “non-coding” DNA which is not use to make essential proteins. Differences in the “standard” sequence often crop up within these regions DNA because they don’t affect the health or survival of the cell and hence the whole organism. Compare this to situations where a change occurs inside an essential gene, causing it to cease working properly. This is the basis of mutations that cause cancer and other genetic disorders, with the end result that the organism is greatly affected and probably will not survive. The result? The mutation is effectively removed from the gene pool and is not passed on to others in the population.
But in the non-coding regions it’s fine for variation to occur as it doesn’t change how well the organism survives. And this in a nutshell is the key to DNA fnigerprinting. Variation can occur as often as once in every 200 bases. DNA testing examines these changes and can create a discernible pattern of differences, which can be used to assess similarity between two samples.
As I noted above your DNA is arranged in long chains. But we can be separate these long strings by cutting them up, specifically cutting them at the very points where differences in the sequences occur. A second method, which can be used in conjunction with the specific site cutting is to amplify the highly variable pieces by a process known as PCR. The cut up fragments are called bands, which are simply shorter chains of DNA. The number of differently sized bands give each of us unique profile. The more genetic similarity between two samples the more alike the banding patterns will appear, and hence higher the likelihood that the two samples examined are from the same individual.
Why use DNA fingerprinting
Well apart from a convenient plot device for police dram shows on TV, there are many pertinent applications of DNA fingerprinting in the modern world. We can broadly classify these into 3 categories: To examine our ancestry, to discover what where we have been recently, and finally, to predict where we our health and lives may go.
DNA Tests for Relationships
In terms of ancestry testing, DNA fingerprinting is used to investigate our heredity. Since we inherit the arrangement of our DNA from our parents, if we compare the banding patterns of a parent and a child, the test reveals the probability of relatedness; if the two patterns are very similar, then they are probably close family. It’s worth noting though that DNA fingerprinting cannot tell apart identical twins since they of course share exactly the same DNA sequences. When used to complement more traditional sociological methods of determining paternity DNA testing can be used to analyze ancient migration patterns of and claims of historical membership of various ethnicities.
Testing DNA forensically
Fingerprinting DNA can also tell us about recent history. Naturally, the best known examples come from the use of DNA fingerprinting in forensic situations. DNA samples collected at a crime scene can be compared to the DNA of a suspect to indicate conclusively if the suspect was present at that location sometime in the recent past. The laws governing the database archiving of DNA fingerprints vary from state to state and country to country, but generally they only retain data on known offenders, so it is not possible to examine DNA from a crime scene and return the name of the suspect. In a real non-criminal situation, it was discovered that twenty five percent of foods labeled as caviar were actually mixed with cheaper roe from different types of fish. It’s the equivalent of a bar cheating it’s patrons by watering down the drinks. DNA fingerprinting in this case established that the caviar was inferior by identifying DNA from different fish species.
DNA tests for Health
Lastly, fingerprinting DNA can help us forecast our health. DNA tseting is often used to discover the genetic basis disease. If a unique pattern is seen across many unrelated patients with the same disease, then scientists may hone in on the gene or neighborhood of DNA, that might be responsible. Though we are far from developing cures for many genetic disorders, knowing which genes are involved in disease gives valuable clues about how the disorder might work and hence how to tackle finding a cure. Apart from future treatment options, genetic fingerprinting can be use to screen for the disease in people that don’t yet have symptoms, such as pre-natal screening, screening parents and screening fetuses for the presence of inherited abnormalities. See more about medical DNA testing.