Alternative splicing is a fundamental biological process that allows cells to make many different types of mRNAs and proteins from a limited number of genes. For many animals, including humans, it is a feature that is essential for the development of complex cells such as muscles or neurons. A new study finds evidence that the regulation of alternative splicing, which rarely goes wrong in healthy cells, goes haywire in an unexpected place -- the cells of a newly formed embryo. The findings could pave the way for advances in assisted reproductive technologies and stem cell biology.