Cell competition acts as a purifying selection to eliminate cells with mitochondrial defects during early mouse development.

"rna-seq raw as well as processed data are available through arrayexpress accession numbers emtab-8640 for scrna-seq data and e-mtab-8692 for bulk rna-seq data."

"code availability all the code used for generating the figures in the paper is available at https://github com/scialdonelab/cell-competition-paper-figures ."

"Competing Interests: The authors declare no competing interests."

"We would like to thank Stephen Rothery for guidance and advice with confocal microscopy. The Facility for Imaging by Light Microscopy (FILM) at Imperial College London is part-supported by funding from the Wellcome Trust (grant 104931/Z/14/Z) and BBSRC (grant BB/L015129/1). We thank James Elliot and Bhavik Patel from the LMS/NIHR Imperial Biomedical Research Centre Flow Cytometry Facility for support. We are thankful to George Chennell and Alessandro Sardini for guidance and support with Seahorse experiments. Research in Tristan Rodriguez lab was supported by the MRC project grant (MR/P018467/1) and the BBSRC project grant (BB/S008284/1) and by the British Heart Foundation (BHF) PhD studentships (FS/14/62/31288 and FS/17/64/33476). Work in the Scialdone lab is funded by the Helmholtz Association. Ana Lima was funded by a BHF centre of excellence PhD studentship. Shankar Srinivas was funded through Wellcome awards 103788/Z/14/Z and 108438/Z/15/Z."