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