This thesis is about the work I have done in the Luis Lopez-Molina's lab for my master. I have been studying seed dormancy in the highly dormant accession Cvi. Dormancy is an adaptive trait of the freshly produced seed. When a seed is dormant its germination is repressed, thus avoiding the seed to germinate at an inappropriate time. The time of repression varies among the different accession of A.thaliana, the aim of this work was to try to understand what was making these differences During this worked I have performed a screen, a mapping and Seed Coat Bedding Assays. Here you will find more informations about dormancy, the results of my work and its analysis.