Plant Genome IV Conference Plant Genome IV Conference
Hypervariable "minisatellite" regions are abundant in the genomes of many higher eukaryotes, but those of humans have been most extensively studied. The high levels of length polymorphism at many of these loci is due to variation in the number of tandem repeats, and derives from a rate of germline mutation to new length alleles which can be as high as 15% per gamete. In addition to simple variation in length, there is also variation in the distribution of different repeat unit types, such that new mutation is very unlikely to recreate a pre-existing allelic state. The mutation processes which give rise to new variation have been analysed in detail, and have the surprising property of polarity - that is, nearly all mutations observed involve only one extremity of the locus - suggesting that instability is not an intrinsic property of the tandem repeat array, but may instead be directed by elements outside the repeat block. Such extremely variable systems have great power in resolving issues which require high levels of genetic discrimination, and have had uses for many years in determining biological family relationships and the biological origin of evidentiary material. Recent work from our laboratory has made use of this high level of genetic resolution to investigate the worldwide distribution of different evolutionary lineages at one minisatellite locus.