The vast majority of genes in sexually reproducing eukaryotes can recombine during the production of gametes. This reshuffling generates new genotypes that may provide selective advantages. However, reshuffling does not occur among the few genes in the genomes of cytoplasmic organelles (chloroplasts and mitochondria). Instead, these organelles are almost always transmitted through maternal inheritance (1). Why is this phenomenon widespread and how is it achieved? On page 394 of this issue, Zhou et al. (2) solve part of this puzzle by identifying the enzyme that degrades sperm mitochondrial DNA after fertilization.
