Mitochondrial DNA (mtDNA) mutations are maternally inherited and are associated with a broad range of debilitating and fatal diseases. Assisted reproductive technologies designed to uncouple the inheritance of mtDNA from nuclear DNA may enable women who carry mtDNA mutations to have a genetically related child with a greatly reduced risk of disease. Here we report for the first time that pronuclear transplantation (PNT) between normally fertilised human zygotes provides an effective approach to preventing transmission of mtDNA disease. We found that the procedures previously used to perform PNT between abnormally fertilized human zygotes are highly inefficient when applied to those that undergo normal fertilization. We have therefore developed an alternative approach based on transplanting PN shortly after completion of the second meiotic division rather than shortly before onset of the first mitosis. This approach promotes highly efficient development to the blastocyst stage without affecting nuclear genome integrity. Furthermore, the expression profile of genes encoded by the nuclear and mitochondrial genomes was indistinguishable from unmanipulated control embryos. Importantly, levels of mtDNA transferred with the nuclear genome are below the threshold for mtDNA disease. Together these data indicate that transplantation of pronuclei early in the first cell cycle holds promise as a safe and effective approach to preventing transmission of mtDNA disease. Overall design: Single-Cell RNA-seq analysis of embryos generated by pronuclear transfer and unmanipulated control embryos The relationship between single cell samples and the embryo from which they were derived is indicated in the sample ''characteristics: sample type'' field.