"Some organisms such as yeast or social insects are haploid, i.e. they carry a single set of chromosomes. Organisms with a single copy of their genome provide a basis for genetic analyses where any recessive mutation of essential genes will show a clear phenotype due to the absence of a second gene copy. Recessive genetic screens have markedly contributed to our understanding of normal development, basic physiology, and disease. However, all somatic mammalian cells carry two copies of chromosomes (diploidy) that obscure mutational screens. Although deemed impossible, we were able to develop generate mammalian haploid embryonic stem cells, thereby breaking a paradigm of biology.Our novel stem opens the possibility of combining the power of a haploid genome with pluripotency of embryonic stem cells to uncover fundamental biological processes in defined cell types at a genomic scale. The following projects are proposed:1. Towards“yeast” genetics in mammalian stem cells. Development of optimized technologies for rapid, genome-wide screens via repairable mutagenesis. Mutational bar-coding to introduce quantitative genomics to mammalian biology.2. Forward genetic screens to uncover essential stem cell genes, identify novel stemness factors, develop improved systems for iPS cell derivation, and to perform synthetic lethal screens for anti-cancer drugs.3. Reverse genetics using to identify and validate genes involved in cardiovascular physiology, brown and white fat cell development, and pain sensing.4. Hit validation – exemplified by resistance to the bioweapon ricin.Haploid embryonic stem cells carry the promise to revolutionize functional genetics and allow rapid, near whole genome-wide mutational forward genetics analysis and reverse genetics in defined cell types. Our systems will be made available to all researchers and the knowledge gained from our studies should fundamentally impact on the basic understanding of physiology and disease pathogenesis."