The Frozen Zoo
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The Frozen Zoo

By Gwyneth Vandenberg

We are currently living through a sixth mass extinction, with the survival of nearly one million animal and plant species on our planet threatened by harmful human activities. The time to act is now. One of the largest wildlife conservation facilities in the world, known as the Frozen Zoo, is leading the way.

The mission of the Frozen Zoo in San Diego, California is to prevent animal species from disappearing entirely. As of date, the zoo contains samples from over 10,500 individual animals across 1,220 species. To preserve these organisms, scientists collect skin or other tissue samples from threatened wildlife during routine veterinary exams or after the animal has died. They then grow and freeze living cells from these tissues. Freezing cells is a complex procedure that must be executed with great care, as rushing the freezing process can cause ice crystals to form, which may damage cell membranes and cause these tissues to die. To avoid this problem, scientists carefully place these cells in vials and freeze them at an exact temperature of -196°C in tanks filled with stable liquid nitrogen.

These animal tissues, alongside embryos, plant tissues, seeds, and pollen, are genetic resources that can aid conversation efforts. Using these resources, or “germplasm,” scientists can save and reproduce organisms through procedures like vitro oocyte (ovary cell) maturation and fertilization, embryo transfer, and artificial insemination. Conservationists at the Frozen Zoo have seen much success with these methods already. They have successfully created a cheetah embryo by fertilizing an in vitro matured cheetah oocyte with thawed cheetah sperm. The hope is to use these embryos to breed more cheetahs and save them from extinction. Similarly, they have fertilized oocytes from southern white rhinos with sperm that had been frozen for nearly two decades by injecting a single sperm directly into an egg, a process called intracytoplasmic sperm injection. Effective fertilization can help revive the endangered white rhino population and save these special animals from extinction. 

All in all, the preservation efforts of the Frozen Zoo help safeguard our planet’s biodiversity by preventing animal species from going extinct. Who knows which species the Frozen Zoo will save next!


Prisco, J. (2022, March 31). Back from the Brink: How ‘frozen zoos’ could save dying species. CNN. 

United Nations. (n.d.). World is ‘on notice’ as major un report shows one million species face extinction. United Nations.

San Diego Zoo Global’s Frozen Zoo® hits milestone: 10,000 Cell Lines. San Diego Zoo Wildlife Alliance. (n.d.).,placed%20in%20the%20Frozen%20Zoo

Frozen Zoo®. San Diego Zoo Wildlife Alliance. (2018, January 5). 

Cheetah. San Diego Zoo Wildlife Alliance. (2021, April 23). 

White rhino. San Diego Zoo Wildlife Alliance. (2022, August 2). 

Kluth, L. (2023). Frozen Animal Illustration.