DNA fingerprinting techniques used in forensic science are also used today to help track wildlife populations and make management decisions, an approach known as conservation genetics. The technique begins with a sample of DNA. DNA is a double stranded molecule and each strand is made up of a sequence of nucleotides subunits, each of which contains one of four bases: adenine, thymine, cytosine or guanine (identified by letter designations: A, T, C, and G).
Researchers track DNA microsatellites—regions on the DNA molecule where small sequences of DNA bases repeat over and over (called short tandem repeats), such as the T-A-C repeat shown here. Microsatellites are not a functional part of a gene and are not used to produce a protein.
Because they are not functional, microsatellites can accumulate changes without harming the individual. They are passed on to offspring, and the microsatellites in different breeding populations of African elephants are distinct enough to serve as a fingerprint of that population.
In the microsatellite DNA fingerprinting technique, DNA is extracted from the sample in question and many copies of a microsatellite region are produced using a technique known as PCR (polymerase chain reaction).
This is done for each microsatellite region of interest. Researcher Sam Wasser, who studies elephant populations, checks 16 different microsatellites in each elephant's DNA sample. The fragments generated from each different microsatellite region are marked with distinct fluorescent dyes so researchers can tell them apart. Here we show 6 of the 16 microsatellites that Dr. Wasser checks.
The size of each microsatellite is determined by passing the sample through a gel that separates fragments according to size (smaller fragments pass through more quickly than larger ones do). A mixture of microsatellite regions bound to their fluorescent dyes is applied to the top of a thin capillary tube containing the gel. The application of an electrical charge pulls the fragments through the gel. The smaller ones exit first and each microsatellite set is detected as it exits the tube by way of its specific fluorescent dye.
The number of tandem repeats within each microsatellite is then determined based on the size of the fragment. In these two samples, each colored band represents a different microsatellite region and you can see that for these two samples, the length of each microsatellite differs. For instance, the microsatellite region represented in yellow is longer in sample 2 than in sample 1. This means these two samples came from different animals, and in this case, different populations.
The banding patterns from individuals from different populations are unique enough to be "fingerprints," identifying which population the sample probably came from. Dr. Wasser has created has created a reference map of elephant populations in Africa based on microsatellite analysis. The microsatellite pattern in confiscated or black market ivory can be compared to this reference map, identifying poaching "hotspots."
Compare this unknown sample to the two reference samples shown here. Which population did this sample come from?