De-extinction

De-extinction, also known as resurrection biology, or species revivalism is the process of creating an organism, which is either a member of, or resembles an extinct species, or breeding population of such organisms. Cloning is the most widely proposed method, although selective breeding has also been proposed. Similar techniques have been applied to endangered species. De-extinction, also known as resurrection biology, or species revivalism is the process of creating an organism, which is either a member of, or resembles an extinct species, or breeding population of such organisms. Cloning is the most widely proposed method, although selective breeding has also been proposed. Similar techniques have been applied to endangered species. There is significant controversy over de-extinction. Critics assert that efforts would be better spent conserving existing species, that the habitat necessary for formerly extinct species to survive is too limited to warrant de-extinction, and that the evolutionary conservation benefits of these operations are questionable. Cloning is the method discussed as an option for bringing back extinct species, by extracting the nucleus from a preserved cell from the extinct species and swapping it into an egg of the nearest living relative. This egg can then be inserted into a relative host. It is important to note that this method can only be used when a preserved cell is available. This means that it is most feasible for recently extinct species. Although de-extinction efforts have not yet succeeded in producing viable offspring of a previously extinct species, the same process has been applied successfully to endangered species. The banteng is an endangered species that was successfully cloned, and the first to survive for more than a week (the first was a gaur that died two days after being born). Scientists at Advanced Cell Technology in Worcester, Massachusetts, United States extracted DNA from banteng cells kept in the San Diego Zoo's 'Frozen Zoo' facility, and transferred it into eggs from domestic cattle, a process called somatic cell nuclear transfer. Thirty hybrid embryos were created and sent to Trans Ova Genetics, which implanted the fertilized eggs in domestic cattle. Two were carried to term and delivered by Caesarian section. The first hybrid was born on April 1, 2003, and the second two days later. The second was euthanized, but the first survived and, as of September 2006, remained in good health at the San Diego Zoo. Scientists from the University of Newcastle and the University of New South Wales, including Andrew French, Michael Mahony, Simon Clulow and Mike Archer reported in May 2013 the successful cloning of the extinct frog Rheobatrachus silus using the process of somatic cell nuclear transfer. The embryos developed for several days but died. In an important development the scientists from Newcastle reported associated technologies that provide a 'proof of concept' for the proposal that frozen zoos (also referred to as genome banks and seed banks) are an effective mechanism to provide an insurance against species extinction and the loss of population genetic diversity. They connected the circle between de-extinction and the prevention of extinction for threatened animal species. The important advances were the capacity to successfully recover live frozen embryonic cells from animals that produce large yolky eggs (anamniotes such as fishes and amphibians) When this development is combined with somatic cell nuclear transfer (SCNT) it enables the genome to be recovered. The scientists point out that many embryonic cells can be frozen and when combined with frozen sperm storage enables the genetic diversity of populations to be stored. With groups of vertebrates such as the amphibians facing an extinction crisis they propose this as an effective means to prevent extinction while the causes of declines can be identified and remedied. The technical difference between frozen tissue samples commonly used for genetic studies (e.g. phylogenetic reconstruction) and those in a frozen zoo is the use of cryoprotectants and special freezing rates at the time of freezing and thawing. With recent, rapid advances in genome sequencing and assembly, and gene editing with CRISPR-Cas9, it may soon be possible to insert relevant genes from extinct species into the genomes of their closest extant relatives. Germ cells may be edited directly, so that the egg and sperm produced by the extant parent species will produce offspring of the extinct species, or somatic cells may be edited and transferred via somatic cell nuclear transfer. Because it is possible to sequence and assemble the genome of extinct organisms from highly degraded tissues, this technique enables scientists to pursue de-extinction in a wider array of species, including those for which no well-preserved remains exist. While the methods needed to carry out genome editing for de-extinction are advancing, there are still several limitations. First, the more degraded and old the tissue from the extinct species is, the more fragmented the resulting DNA will be, making genome assembly more challenging. Additionally, a close relative must be living and able to be reared in captivity for insertion of edited cells. Because a near relative is used as a host for the edited cells, the resulting individuals will not be exactly the same as the extinct species, but may also possess traits of the extant relative. Selective breeding is the process by which living relatives of the extinct species are identified and specifically mated to reproduce the traits of the extinct species. This method can recreate the traits of an extinct species, but the genome will differ from the original species. The aurochs, which became extinct in 1627, could possibly be brought back by taking DNA samples from bone and teeth fragments in museums in order to obtain genetic material to recreate its DNA. Researchers would then compare the DNA to that of modern European cattle to determine which breeds still carry the creature's genes, and then undertake a selective breeding program to reverse the evolutionary process. The intention would be that with every passing generation, the cattle would more closely resemble the ancient aurochs.The quagga, a subspecies of zebra which has been extinct since the 1880s, has been revived using selective breeding of zebras. Since the new animal is not genetically identical to the extinct subspecies, the new animal is called the Rau quagga.