Classes of VNTRs
There are two principal families of VNTRs: microsatellites and minisatellites. The former are repeats of sequences less than about 5 base pairs in length (an arbitrary cutoff), while the latter involve longer blocks. Confusing this distinction is the recent use of the terms Short Tandem Repeat (STR) and Simple Sequence Repeat (SSR), which are more descriptive, but whose definitions are similar to that of microsatellites. VNTRs with very short repeat blocks may be unstable - dinucleotide repeats may vary from one tissue to another within an individual, while trinucleotide repeats have been found to vary from one generation to another (see Huntington's disease). The 13 assays used in the CODIS database are usually referred to as STRs, and most analyze VNTRs that involve repeats of 4 base pairs.
Read more about this topic: Variable Number Tandem Repeat
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