Birds have no such incubation chamber. There is no uterus equivalent in which to stick a bird clone embryo. Currently, without the ability to cryopreserve the cells of bird species and clone them later, there is no scientific failsafe for birds like there is for mammals in case of genetic bottlenecks or critical endangerment.
However, Jensen is hoping a different emerging genetic technology could perform a similar role for endangered bird species. This one focuses not on creating an entire clone, but on altering what kinds of chicks an individual is producing.
That requires researchers to focus on birds' testes and ovaries, also called the gonads. Cloning a mammal involves inserting the DNA of one individual into one egg, and producing one offspring that is the genetic replica of the donor. Reseearchers refer to these hybrid animals as chimeras.
To make a chimera, researchers carefully insert PGCs from a donor into a host embryo as it is developing. If everything goes to plan, the host will grow up to become an adult that produces sperm or eggs containing the DNA of the donor. So, for instance, you might have a domestic rooster host who produces sperm with the DNA of a Greater Prairie-Chicken. If the rooster were mated with a female Greater Prairie-Chicken, the pair could then produce Greater Prairie-Chicken chicks.
This approach has the benefit that one host parent could theoretically produce many offspring with the DNA of a donor over the course of its lifetime, rather than the single individual that would be produced via cloning. And, as long as researchers can cryopreserve these PGCs, this can still offer the benefit of bringing back DNA from a donor that died long ago. Researchers have made some progress, however, that makes Jensen and Novak hopeful that the technology could one day be used for conservation.
Most of the research thus far has involved domestic chickens. In , researchers produced the first clone of an endangered species: a type of Asian ox known as a guar.
Sadly, the baby guar, which had developed inside a surrogate cow mother, died just a few days after its birth. In , another endangered type of ox, called the Banteg, was successfully cloned.
Soon after, three African wildcats were cloned using frozen embryos as a source of DNA. Although some experts think cloning can save many species that would otherwise disappear, others argue that cloning produces a population of genetically identical individuals that lack the genetic variability necessary for species survival.
Some people also have expressed interest in having their deceased pets cloned in the hope of getting a similar animal to replace the dead one.
But as shown by Cc the cloned cat, a clone may not turn out exactly like the original pet whose DNA was used to make the clone. Reproductive cloning is a very inefficient technique and most cloned animal embryos cannot develop into healthy individuals. For instance, Dolly was the only clone to be born live out of a total of cloned embryos. This very low efficiency, combined with safety concerns, presents a serious obstacle to the application of reproductive cloning.
Researchers have observed some adverse health effects in sheep and other mammals that have been cloned. These include an increase in birth size and a variety of defects in vital organs, such as the liver, brain and heart. Other consequences include premature aging and problems with the immune system.
Another potential problem centers on the relative age of the cloned cell's chromosomes. As cells go through their normal rounds of division, the tips of the chromosomes, called telomeres, shrink. Over time, the telomeres become so short that the cell can no longer divide and, consequently, the cell dies. This is part of the natural aging process that seems to happen in all cell types.
As a consequence, clones created from a cell taken from an adult might have chromosomes that are already shorter than normal, which may condemn the clones' cells to a shorter life span. Indeed, Dolly, who was cloned from the cell of a 6-year-old sheep, had chromosomes that were shorter than those of other sheep her age. Dolly died when she was six years old, about half the average sheep's year lifespan.
Therapeutic cloning involves creating a cloned embryo for the sole purpose of producing embryonic stem cells with the same DNA as the donor cell. These stem cells can be used in experiments aimed at understanding disease and developing new treatments for disease. To date, there is no evidence that human embryos have been produced for therapeutic cloning. The richest source of embryonic stem cells is tissue formed during the first five days after the egg has started to divide.
At this stage of development, called the blastocyst, the embryo consists of a cluster of about cells that can become any cell type. Stem cells are harvested from cloned embryos at this stage of development, resulting in destruction of the embryo while it is still in the test tube. Researchers hope to use embryonic stem cells, which have the unique ability to generate virtually all types of cells in an organism, to grow healthy tissues in the laboratory that can be used replace injured or diseased tissues.
In addition, it may be possible to learn more about the molecular causes of disease by studying embryonic stem cell lines from cloned embryos derived from the cells of animals or humans with different diseases. Finally, differentiated tissues derived from ES cells are excellent tools to test new therapeutic drugs.
Many researchers think it is worthwhile to explore the use of embryonic stem cells as a path for treating human diseases. Because she was the first mammal to be cloned from an adult cell, rather than an embryo. This was a major scientific achievement, but also raised ethical concerns.
Since , when Dolly was born, other sheep have been cloned from adult cells, as have mice, rabbits, horses and donkeys, pigs, goats and cattle. In a mouse was cloned using a nucleus from an olfactory neuron, showing that the donor nucleus can come from a tissue of the body that does not normally divide.
Producing an animal clone from an adult cell is obviously much more complex and difficult than growing a plant from a cutting. So when scientists working at the Roslin Institute in Scotland produced Dolly, the only lamb born from attempts, it was a major news story around the world.
To produce Dolly, the scientists used the nucleus of an udder cell from a six-year-old Finn Dorset white sheep. The nucleus contains nearly all the cell's genes. Then they injected the cell into an unfertilised egg cell which had had its nucleus removed, and made the cells fuse by using electrical pulses.
The unfertilised egg cell came from a Scottish Blackface ewe. When the scientists had managed to fuse the nucleus from the adult white sheep cell with the egg cell from the black-faced sheep, they needed to make sure that the resulting cell would develop into an embryo. They cultured it for six or seven days to see if it divided and developed normally, before implanting it into a surrogate mother, another Scottish Blackface ewe.
Dolly had a white face. From cell fusions, 29 early embryos developed and were implanted into 13 surrogate mothers. But only one pregnancy went to full term, and the 6. The main reason that the scientists at Roslin wanted to be able to clone sheep and other large animals was connected with their research aimed at producing medicines in the milk of such animals. Researchers have managed to transfer human genes that produce useful proteins into sheep and cows, so that they can produce, for instance, the blood clotting agent factor IX to treat haemophilia or alphaantitrypsin to treat cystic fibrosis and other lung conditions.
Cloned animals could also be developed that would produce human antibodies against infectious diseases and even cancers. Even before cloning, black-footed ferrets were a conservation success story. They were thought extinct — victims of habitat loss as ranchers shot and poisoned off prairie dog colonies that made rangelands less suitable for cattle — until a ranch dog named Shep brought a dead one home in Wyoming in Scientists gathered the remaining population for a captive breeding program that has released thousands of ferrets at dozens of sites in the western U.
Lack of genetic diversity presents an ongoing risk. Eventually scientists may be able to modify those genes to help cloned animals survive. Cloning makes a new plant or animal by copying the genes of an existing animal.
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