Simple Repeat Loci as Tools for Genetic Identification

Abstract

The genomes of eukaryotic organisms harbor two principally different classes of DNA: Single-copy DNA is present once per haploid chromosome set, whereas repetitive DNA can exist in a few to a few hundred thousand (or million) copies. The whole array of repetitive sequences may comprise from less than 10% to more than 90% of the genome in different animal or plant species (in man it is about 30%). Novel names have been given to several subclasses of repetitive DNA elements: SINES and LINES represent supergroups of short and long interspersed nucleotide elements, rather loosely defined on the basis of length (for a general review see, e.g., Epplen 1988; Singer 1982). Some designations for more narrowly defined groups reflect their discoverers’ whim. After the sputniks had been successfully launched and Yuri Gagarin came back from space, the term satellite DNA was coined to designate the sizeable amount (up to 30%) of a eukaryotic genome that can be separated by buoyant density gradient centrifugation. For the present discussion, minisatellites and microsatellites are of special interest: the expression “minisatellites” was established in order to distinguish a particular kind of tandemly reiterated repeat with a basic unit of roughly 33 base pairs from all others (Jeffreys et al. 1985); later, the designation “microsatellites” caught on, somewhat unfortunately, for tandemly organized stretches of dinucleotides which are amplified by the polymerase chain reaction (PCR). Variable number of tandem repeats (VNTRs) is commonly used to name both entities of sequences.