Introduction; From nature to agriculture: why we need diversity?; Microrganisms and pests associated to plants; Genetic markers and molecular markers; How measures are taken: a brief review on the simplest and most popular tools; Random amplified DNA reveals polymorphism; Repetitive sequences can be especially polymorphic; Sequencing and single nucleotide polymorphism; Markers may help to understand evolution; The gains in plant breeding depends of variance; Conclusion
