Use of Hypervariable Markers in Genetic Diversity Studies

Abstract. Hypervariable markers (also called minisatellite markers or VNTRs--Variable Number of Tandem Repeats) were first identified in humans and consist of arrays of tandemly repeated sequences. Sequences hybridizing to human minisatellites or other sequences, such as the M13 phage, have since been identified in many other organisms, particularly plants. Our investigations in common bean (Phaseolus vulgaris) have revealed the following about sequences hybridizing to M13: 1) M13-related sequences reveal high levels of polymorphisms compared to other sequences, particularly RFLPs and isozymes; 2) they provide evidence for a reduction in diversity during and after domestication, particularly as a consequence of modern breeding efforts; 3) they reveal patterns of genetic organization of the species similar to those identified with other markers; 4) their linkage relationships to other markers suggest that they may be preferentially located at the end of linkage groups; 5) sequencing of a common bean sequence hybridizing to M13 does not reveal the characteristic tandem repeat pattern but rather a complex array of imperfect direct and inverted repeats. These results will be discussed in light of results obtained with other organisms.