As many as one million black-footed ferrets lived on the continent in the late 1800s, but by the late 1950s, the species was presumed extinct. Scientists discovered a wild population in 1964, but even that group died out, and a captive breeding effort failed. Since a second rediscovery of a wild population in 1981, conservationists have worked hard to conserve the species using traditional breeding programs as well as more innovative technologies, including freezing semen and cloning.

One of the challenges conservationists face when tasked with bringing back a species from the brink of extinction is limited genetic diversity, which leads to inbreeding and can make offspring more vulnerable to issues, including hereditary abnormalities, poor reproductive efficiency and increased mortality rates.

The current population of black-footed ferrets—thousands of which have been reintroduced across the western U.S. since the 1990s—is all descend from just seven individuals, except for a few clones and Antonia’s new offspring. That’s a recipe for genetic bottlenecks that threaten the longevity of the species.

Cue cloning. In 1988, scientists had the foresight to collect tissue samples from a black-footed ferret named Willa after she died and preserve the material in the Frozen Zoo at the San Diego Zoo Wildlife Alliance. Willa never reproduced, so her genetic material was not included in the modern ferret population. Her preserved genes contain three times more genetic diversity than living black-footed ferrets do.