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Early 20th-Century

Although Dolly is generally recognized as the first animal to be cloned using this technique, earlier instances of SCNT exist as early as the 1950s. In particular, the research of Sir John Gurdon in 1958 entailed the cloning of Xenopus laevis utilizing the principles of SCNT. In short, the experiment consisted of inducing a female specimen to ovulate, at which point her eggs were harvested. From here, the egg was enucleated using ultra-violet irradiation to disable the egg's pronucleus. At this point, the prepared egg cell and nucleus from the donor cell were combined, and then incubation and eventual development into a tadpole proceeded. Gurdon's application of SCNT differs from more modern applications and even applications used on other model systems of the time (i.e., Rana pipiens) due to his usage of UV irradiation to enucleate the egg instead of using a pipette to remove the nucleus from the egg.