A purebred Yellowstone bison calf is growing up at the Bronx Zoo after scientists implanted a genetically pure embryo into a surrogate bison mom.

The surrogate gave birth to a healthy male calf at the zoo on June 20. The embryo had been taken from a Yellowstone bison, washed free of disease and implanted in the surrogate.

While many bison have been bred with cattle, Yellowstone has one of the world’s largest and most genetically pure bison herds. However, about 40 percent test positive for exposure to brucellosis, which can cause pregnant animals to miscarry. Concern about the disease has prevented the animals from being taken out of the park to reproduce.