The somatic cell donor was a Przewalski's horse stallion named Kuporovic, born in the UK in 1975, and relocated three years later to the US, where he died in 1998. Due to concerns over the loss of genetic variation in the captive Przewalski's horse population, and in anticipation of the development of new cloning techniques, tissue from the stallion was cryopreserved at the San Diego Zoo's Frozen Zoo. Breeding of this individual in the 1980s had already substantially increased the genetic diversity of the captive population, after he was discovered to have more unique alleles than any other horse living at the time, including otherwise-lost genetic material from two of the original captive founders. To produce the clone, frozen skin fibroblasts were thawed, and grown in cell culture. An oocyte was collected from a domestic horse, and its nucleus replaced by a nucleus collected from a cultured Przewalski's horse fibroblast. The resulting embryo was induced to begin division, and was cultured until it reached the blastocyst stage, then implanted into a domestic horse surrogate mare, which carried the embryo to term and delivered a foal with the Przewalski's horse DNA of the long-deceased stallion.