Telomeres are the repeated sequences found at chromosome extremities. They are essential for genome integrity and control of cell proliferation. Telomere length (TL) at one chromosome end is a dynamic parameter subject to both shortening and elongation during cell divisions, thus resulting in a population-level distribution. Additionally, the TL distribution can be different at each chromosome end and the aggregated TL distribution over all ends in an isogenic population of cells is therefore a complex genomic property. How are the TL distributions at individual chromosome ends and aggregated over all ends regulated? What are the genetic determinants in trans and cis that control the natural diversity of TL and how do they interact with the environment? What are the fitness components associated with the natural TL diversity? To address these questions, our proposal DONATELO will leverage the natural diversity of Saccharomyces cerevisiae strains and the single molecule long-read sequencing technology that enable the measurement of TL distributions at each chromosome end. We recently established a large panel of high quality genome assemblies for 142 strains representing the phylogenetic and ecological diversity of the S. cerevisiae species, called the S. cerevisiae Reference Assembly Panel (ScRAP) (O’Donnell et al., 2023). DONATELO will (i) characterize the TL distributions and their stability across the genetically diverse ScRAP strains, as well as in an extended panel of strains, and various environmental conditions, (ii) uncover new genetic determinants of TL by tapping into the variants found in the ScRAP and the extended panel, and (iii) measure the phenotypes resulting from TL variations. In terms of approaches, our proposal will make the most of yeast genetics, genome engineering, Nanopore sequencing, bioinformatics and mathematical modelling. Overall, we anticipate that DONATELO will advance our understanding of telomere regulation and will address the fundamental question of whether and how this regulation is adaptive.