![]() Neither Najin nor Fatu is thought to be capable of a safe pregnancy, so the embryos will instead be entrusted to female southern white rhinos, a related species with a healthy wild population. The next step will be to transfer embryos to a surrogate. Four developed into viable embryos, bringing the total number of frozen embryos to nine. A total of 19 oocytes were obtained from Fatu 14 were fertilised with sperm from Suni, a male who died in 2014. The most recent egg collection was performed on March 28th. Any embryos that successfully develop in the dish are placed in liquid nitrogen for safe-keeping until such a time as the team is ready to implant them into a womb. They are then placed in a specially designed incubator equipped with a camera that allows the team to monitor the cells as they develop. Sperm are injected through a needle directly into the eggs. The oocytes are immediately flown to Italy, where they are fertilised with thawed sperm from a dead male whose cells are banked in Germany. Five times since 2019, a team of researchers, conservationists, park rangers and veterinarians have gathered in the park to harvest oocytes (immature egg cells) from the ovaries of one or both females, who are placed under general anaesthetic for the procedure. ![]() The first approach, led by a group called BioRescue, uses a version of in-vitro fertilisation involving rather more international travel than most human procedures. Nevertheless, at a meeting in Vienna in 2015, researchers agreed on a twin-track approach to de-extinction. The northern white rhino is what is known as “functionally extinct”: the last male, Sudan, died in 2018, leaving behind just two females, a mother-and-daughter pair in Kenya, dubbed Najin and Fatu. They contain the remains of not one but 12 northern white rhinoceroses, five males and seven females. But alongside them in San Diego are tubes that hold a different promise. The po’ouli’s frozen cells, therefore, are unlikely ever to give rise to a new population of birds. Efforts to rescue a species from the brink of extinction must begin long before it is reduced to just one individual, or even three. Even if it had lived, it could only ever have given rise to a population of clones, the opposite of biological diversity, for which genetic diversity is essential. Its DNA was primarily inherited from a single individual. The technique that produced the short-lived bucardo kid was similar to that used to create Dolly, a cloned sheep, in 1996. It was delivered by caesarean section in 2003, but lived for only “some minutes”, according to an account in the journal Theriogenology. Over 200 embryos were transferred to the wombs of surrogate domestic goats, leading to just one live birth. Using a zap of electricity, they fused the DNA with the egg’s cellular “shell” and produced more than 400 embryos, all carrying the goat’s genes. The team removed the bundle of DNA from inside those cells and injected it into the emptied eggs of a domestic goat. A skin biopsy taken from the last female had produced live cells. In 2009, a team of researchers announced they had delivered the kid of a bucardo, a species of wild goat that had gone extinct nine years earlier. Dr Ryder and others are developing techniques that might, theoretically, make it possible to create a live newborn long after the last members of its species have died.
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