Abstract Sexual reproduction is a widely spread feature of eukaryotes and was already present in the last eukaryotic common ancestor. While most extant eukaryotes inherit mitochondria from a single parent, the mechanisms enforcing uniparental inheritance vary widely. The first eukaryotes likely would not have evolved such mechanisms yet, so cellular fusion would have led to mitochondrial mixing (biparental inheritance). Here, we explore the evolutionary consequences of biparental inheritance of