The cells generated by the very first division of the fertilized egg make a lopsided contribution to the body’s organs and tissues.

This study performed lineage tracing of live human embryos from the first cleavage division until the blastocyst stage and discovered that the majority of cells in the EPI, the future human body, originate from one of the two cells in most embryos. The first blastomere to divide at the 2-cell stage has a higher likelihood to generate the first, and more, internalized cells at the 8-to-16-cell stage.

https://www.cell.com/cell/fulltext/S0092-8674(24)00455-0?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867424004550%3Fshowall%3Dtrue (open access)