| DNA testing is done for many different reasons. DNA | | | | As DNA testing has evolved over time, the testing |
| evidence can link an alleged criminal to a crime scene. | | | | methods have become more precise and are able to |
| DNA paternity and maternity testing can identify a | | | | work with much smaller DNA samples. Early DNA |
| child's father or mother. DNA relationship testing can | | | | testing was done using dime-size drops of blood. |
| determine if two individuals are full or half siblings. DNA | | | | Today's tests can extract DNA from the back of a |
| ancestry testing can determine ethnic origins and | | | | licked stamp. The DNA must be extracted from |
| genealogical roots. | | | | whatever sample is provided. DNA must be isolated |
| How DNA testing is done depends on the results | | | | and purified before it can be compared. In essence, it |
| desired and the samples available. DNA fingerprinting | | | | has to be "unlocked" from the cell in which it exists. |
| (or profiling as it's also known) is the process of | | | | The cell walls are usually dissolved with a detergent. |
| analyzing and comparing two DNA samples. Only | | | | Proteins in the cell are digested by enzymes. After this |
| identical twins have the exact same DNA sequence, | | | | process, the DNA is purified, concentrated, and tested. |
| everyone else's DNA is unique. This makes DNA the | | | | DNA testing is done most often today using a process |
| perfect way to link individuals to each other or to | | | | called "short tandem repeats," or STR. Human DNA |
| locations where they have been. | | | | has several regions of repeated sequences. These |
| The entire DNA chain is incredibly long, much to long to | | | | regions are found in the same place on the DNA chain, |
| examine all of it. Human DNA is made up of about 3.3 | | | | but the repeated sequences are different for each |
| billion base pairs. The differences between DNA | | | | individual. The "short" tandem repeats (repeated |
| samples occur only in small segments of the DNA--the | | | | sequences of two to five base pairs in length) have |
| rest of the DNA is pretty much the same. DNA testing | | | | been proven to provide excellent DNA profiling results. |
| focuses on those segments that are known to differ | | | | STR is highly accurate--the chance of misidentification |
| from person to person. | | | | being one in several billion. |