What was cloned after dolly

This research suggested two protocols for nuclear transfer in sheep that are expected to produce embryos with normal ploidy. In one, the oocyte is activated before enucleation and transfer of a nucleus, which may be at any stage of the cycle. In this case, the transferred nucleus determines whether or not DNA replication occurs. In the second protocol, nuclei that are awaiting DNA replication are transferred into oocytes in metaphase II of meiosis.

In this case, DNA replication occurs in an appropriate manner because the transferred nucleus is awaiting replication and the cytoplast is primed to carry out the replication. All other combinations are expected to lead to errors of one kind or another and have to have limited developmental potential. This initial analysis defined procedures that yield embryos with normal ploidy. This difference is thought to reflect the greater efficiency with which the oocyte cytoplasm reprograms gene expression of the transferred somatic cell nucleus to that of an early embryo.

Production of embryonic cells in G1-phase is time-consuming and not entirely accurate. This is particularly the case for embryo-derived cells, which do not respond to the normal checkpoints. Keith Campbell introduced the use of cultured cells in G0, through which tissue-derived cells exit the cell cycle and become quiescent if cultured in a low concentration of serum. In this case, the quiescent cells are in a stable state and can be left in an incubator or on the bench for as long as nuclei are required for transfer.

This innovation facilitated nuclear transfer and yielded more reproducible results. Credit: Nick Higgins. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science.

Read more from this special report: Whatever Happened to Cloning? Get smart. Sign up for our email newsletter. Sign Up. Support science journalism. Knowledge awaits. In , Snuppy fathered his own puppies, the article said. In , researchers in Japan announced that they had cloned mice using cells that had been frozen at minus 4 degrees Fahrenheit minus 20 degrees Celsius for 16 years. After thawing these cells, researchers found that all of them had ruptured, but the scientists were still able to extract the DNA required to produce healthy cloned mice, according to the study, published in in the journal Proceedings of the National Academy of Sciences.

The scientists wrote that they hoped that this might indicate that it would be possible, in future, to "resurrect," certain animals or keep stocks of frozen tissue to use later, the study said. In , resurrection science got another boost: Scientists reported that, for the first time, they had cloned an extinct mammal, the bucardo a type of wild goat also called a Pyrenean ibex. The group of researchers, with members from Spain, France and Belgium, used cells from preserved samples from a bucardo captured in to produce the cloned animal, according to the study.

However, the young goat died only minutes after its birth because of defects in her lungs. The research was published in in the journal Theriogenology. Two halves make a whole. From that moment forward, nearly all cells in that body have the same genetic makeup. When the one-cell embryo duplicates its genetic material, both cells of the now two-cell embryo are genetically identical. When they in turn duplicate their genetic material, each cell at the four-cell stage is genetically identical.

In this process, researchers remove the genetic material from an egg and replace it with the nucleus of some other body cell.

The resulting egg becomes a factory to produce an embryo that develops into an offspring. No sperm is in the picture; instead of half the genetic material coming from a sperm and half from an egg, it all comes from a single cell. Dolly was the culmination of hundreds of cloning experiments that, for example, showed diploid embryonic and fetal cells could be parents of offspring. But there was no way to easily know all the characteristics of the animal that would result from a cloned embryo or fetus.

Researchers could freeze a few of the cells of a cell embryo, while going on to produce clones from the other cells; if a desirable animal was produced, they could thaw the frozen cells and make more copies.

But this was impractical because of low success rates. Dolly demonstrated that adult somatic cells also could be used as parents. Thus, one could know the characteristics of the animal being cloned. By my calculations, Dolly was the single success from tries at somatic cell nuclear transfer.

Sometimes the process of cloning by somatic cell nuclear transfer still produces abnormal embryos, most of which die. These days most cloning is done using cells obtained by biopsying skin.