Microsatellite Analysis

Microsatellites, also known as STRs (short tandem repeats), are tandem repeats of a simple dinucleotide, trinucleotide, tetranucleotide, pentanucleotide, or hexanucleotide sequence (two to six bases) that occur abundantly and at random throughout most eukaryotic genomes (roughly one microsatellite every 10 kb). They are typically short (often less that 100 bp long) and embedded within unique sequence, thus being ideal for designing flanking primers for in vitro amplification by the polymerase chain reaction (PCR) (see Chapter 6 ). The high degree of polymorphism, as a result of variation in the number of repeat units, and the stability displayed by microsatellites make them perfect markers for use in constructing high-resolution genetic maps to identify susceptibility loci involved in common genetic diseases (1 ). In addition to their applications in genome mapping and positional cloning, these markers have been applied in fields as diverse as tumor biology, personal identification, population genetic analysis, and the construction of human evolutionary trees. To appreciate the impact that microsatellite analysis has had within the medical field, search PubMed for “microsatellite” on the National Center for Biotechnology Information website www.ncbi.nlm.nih.gov and thousands of entries will be found. References can be found that date back more than 20 yr. Today, microsatellites are still being used extensively to investigate the genome although rapid advances in technology have seen many modifications to the original methods.