EXPERIMENT   Frog egg cells are exposed to UV light, destroying the nucleus. Nuclei from cells of embryos are transplanted into the enucleated egg cells.

 RESULTS   Most of the recipient eggs developed into tadpoles when the transplanted nuclei came from relatively undifferentiated cells of an early embryo.

 CONCLUSION   The nucleus from a differentiated frog cell can direct development of a tadpole. However, its ability to do so decreases as the donor cell becomes more differentiated.