A minisatellite is a small portion of the deoxyribonucleic acid (DNA) macromolecule responsible for coding and transferring human genetic characteristics. This molecule is made up of a ladder-like structure of alternating base pairs of phosphate and deoxyribose molecules. In the case of a minisatellite, only 10 to 60 base pairs often exist, but sometimes 100 or more may be present. These minisatellites are known to exist at more than 1,000 locations in the human genome, which codes for all the genetic traits of an organism.
The first minisatellite molecule was discovered by A.R. Wyman and R. White at the National Institutes of health (NIH) in the United States, in 1980. This led to their use for the practice of DNA fingerprinting in crime forensics early on. They were later discovered to be hypervariable or hypermutable, with a basic average mutation rate of up to 20%. This classified the minisatellite as the most unstable region of the human genome.
Microsatellite portions of DNA also exist, where genetic sequences are composed of only two to five base pairs. Due to the fact that both the minisatellite and microsatellite structures are highly variable and have high mutation rates, they are used frequently in a variety of research. Purposes they are used for include the legal identification of the genetic parents of an individual, mapping genetic variations in the human population, and in the study of cancer. Long arrays of minisatellite that are over 100 base pairs in length are considered very unstable. Research in mice has shown they have up to a 100% mutation rate, especially in the cerebellum portion of the brain.
The reason that minisatellite DNA is considered inherently unstable is that it is a repeated sequence of DNA base pairs that doesn't appear to code for any expressed genetic traits. These minisatellite molecules are present in a wide variety of animals and other organisms, such as bacteria. Like introns, which are noncoding segments of DNA as well, minisatellite DNA serves no understood function. They have, however, been associated with disorders such as Huntington's disease and various cancers.
One possible purpose for minisatellite DNA might be the role they play where they exist on the end of telomeres. A telomere is a segment of DNA on the end of a chromosome that serves to protect the chromosome from damage and from losing genetic coding sequences that are used in the process of cell division. The shortening of telomeres is known to contribute to the aging process, and lab experiments to extend telomere length have made it possible to keep cells healthy beyond their normal lifespan. In fact, the enzyme telomerase that maintains telomeres is activated by cancer cells as well, giving them a level of virtual immortality.
