Single-gender worlds will remain a sci-fi fantasy. Gay and lesbian couples won’t become parents this way for the foreseeable future. This kind of manipulation is just too risky for humans. But unisexually reproducing mice are an impressive accomplishment, and CRISPR stands out again as a powerful research tool, opening up brand new possibilities for the study of genomic imprinting. For further details, please see the STAT News article about the Cell Stem Cell paper by Zhi-Kun Li.