The article revisits the mitochondrial genome, which contains genes derived from an alphaproteobacterial endosymbiont. Despite the initial presence of thousands of protein-coding genes, only 1 to about 70 remain in extant mitochondrial genomes (mitogenomes). The review explores the characteristics of mitochondria-to-nucleus gene transfer and the resulting varied content of mitogenomes across eukaryotes. It introduces a 'burst-upon-drift' model to explain nuclear-mitochondrial population genetics, where flares of transfer occur due to genetic drift. The article discusses the CoRR hypothesis and the hydrophobicity hypothesis, which attempt to explain why certain genes are retained in mitogenomes. However, both hypotheses fail to fully account for the diversity of coding content. The authors propose that the spurt-like evolution of mitogenome content is an indicator of ancient bottlenecks that led to rapid wholesale nuclear migration of many mitogenes, especially when mitochondria were temporarily released from energetic demands.The article revisits the mitochondrial genome, which contains genes derived from an alphaproteobacterial endosymbiont. Despite the initial presence of thousands of protein-coding genes, only 1 to about 70 remain in extant mitochondrial genomes (mitogenomes). The review explores the characteristics of mitochondria-to-nucleus gene transfer and the resulting varied content of mitogenomes across eukaryotes. It introduces a 'burst-upon-drift' model to explain nuclear-mitochondrial population genetics, where flares of transfer occur due to genetic drift. The article discusses the CoRR hypothesis and the hydrophobicity hypothesis, which attempt to explain why certain genes are retained in mitogenomes. However, both hypotheses fail to fully account for the diversity of coding content. The authors propose that the spurt-like evolution of mitogenome content is an indicator of ancient bottlenecks that led to rapid wholesale nuclear migration of many mitogenes, especially when mitochondria were temporarily released from energetic demands.