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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Frozen zoo | 2/3 | https://en.wikipedia.org/wiki/Frozen_zoo | reference | science, encyclopedia | 2026-05-05T09:06:16.788437+00:00 | kb-cron |
== Drawbacks == Due to the very low temperatures required, varying levels of stress are put on the DNA samples. Spermatozoa, in particular, are stressed by temperature shock, osmotic stress, and oxidative stress with the latter being the most detrimental. When temperature shock occurs, the membrane is damaged through freezing and thawing of the sperm. Osmotic stress occurs when ice crystals form inside the nucleus during the freezing process, causing differing osmotic pressures within the cell. Oxidative stress is the result of too many reactive oxygen species (ROS), which is highly reactive and damaging to all parts of the cell. Although these stressors are present within the cell, there are solutions to each. By introducing cholesterol to the samples, temperature shock can be reduced. The use of antifreeze proteins provides one solution for osmotic stress. Oxidative stress is the most difficult to combat because of the highly reactive components of ROS, but some measures like adding certain proteins to limit freeze-thaw damage and increase the survival rate of the DNA.
== Applications ==
=== Gaur === A gaur that died of natural causes had some skin cells frozen and added to the San Diego Frozen Zoo. Eight years later, DNA from these cells was inserted into a domestic-cow egg to create an embryo (trans-species cloning), which was then implanted in a domestic cow (Bos taurus). On 8 January 2001, the gaur, named Noah, was born in Sioux Center, Iowa. Noah was initially healthy, but the next day, he came down with clostridial enteritis, and died of dysentery within 48 hours of birth. This is not uncommon in uncloned animals, and the researchers did not think it was due to the cloning.
=== Banteng === The banteng was the second endangered species to be successfully cloned, and the first clone to survive beyond infancy. Scientists at Advanced Cell Technology in Worcester, Massachusetts, extracted DNA from skin cells of a dead male banteng, that were preserved in San Diego 's Frozen Zoo facility, and transferred it into eggs from domestic banteng cows, a process called somatic cell nuclear transfer. Thirty embryos were created and implanted in domestic banteng cows. Two were carried to term and delivered by Caesarian section. The first was born on 1 April 2003, and the second two days later. The second was euthanized, apparently suffering from large offspring syndrome (an overgrowth disorder), but the first survived and lived for seven years at the San Diego Zoo, where it died in April 2010 after it broke a leg and was euthanized.
=== Przewalski's horse clone ===
In 2020, the first cloned Przewalski's horse was born, the result of a collaboration between San Diego Zoo Global, ViaGen Equine and Revive & Restore. The cloning was carried out by somatic cell nuclear transfer (SCNT), whereby a viable embryo is created by transplanting the DNA-containing nucleus of a somatic cell into an immature egg cell (oocyte) that has had its own nucleus removed, producing offspring genetically identical to the somatic cell donor. Since the oocyte used was from a domestic horse, this was an example of interspecies SCNT. 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. The cloned horse was named Kurt, after Dr. Kurt Benirschke, a geneticist who developed the idea of cryopreserving genetic material from species considered to be endangered. His ideas led to the creation of the Frozen Zoo as a genetic library. There is a breeding herd in the San Diego Zoo Safari Park. Once the foal matured, he was relocated to the breeding herd at the San Diego Zoo Safari Park, so as to pass Kuporovic's genes into the larger captive Przewalski's horse population and increase the genetic variation of the species. In 2023, a second horse, named Ollie, was cloned from the same cell line.
=== Black-footed ferret === To help mitigate inbreeding depression for two endangered species, the Black-footed ferret (Mustela nigripes), Revive & Restore facilitates on-going efforts to clone individuals from historic cell lines stored at the San Diego Zoo Wildlife Alliance Frozen Zoo. The program seeks to restore genetic variation lost from the living gene pool.
On December 10, 2020, the world's first cloned black-footed ferret was born. This ferret, named Elizabeth Ann, marked the first time a U.S. endangered species was successfully cloned. The cells of two 1980s wild-caught black-footed ferrets that never bred in captivity were preserved in the San Diego Wildlife Alliance Frozen Zoo. One of them was cloned to increase genetic diversity in this species in December 2020. More clones of both are planned. They will initially be bred separately from the non-cloned population.
=== Pyrenean ibex ===