Arthritis also affects the soft tissue in a joint, so Sinclair notes the bones alone do not point to a conclusive diagnosis or lack thereof. And Dolly really did limp. Fears about prematurely aging clones may be greatly exaggerated. Telomeres are repetitive DNA sequences at the ends of chromosomes, and they are shortened every time a cell divides. Since then, scientists have cloned a whole menagerie of animals: mice, horses, cattle, pigs, dogs, and so on.
Studies of their telomere lengths have turned up every possible result: Clones have shorter telomeres , clones have longer telomeres , and clones have normal telomeres —depending on the species or cloning technique. Clones do have unique health problems, just not the ones that dominated headlines about Dolly. Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article.
Provided by the Springer Nature SharedIt content-sharing initiative. Advanced search. Skip to main content Thank you for visiting nature. Download PDF. You have full access to this article via your institution. References 1 Schon, E. Article Google Scholar Download references. Authors Henry Gee View author publications.
Rights and permissions Reprints and Permissions. About this article Cite this article Gee, H. Copy to clipboard. The explanation lies in the way Dolly was created, by transferring the nucleus of an udder cell from one sheep and inserting it into another ewe's egg cell that had its own nucleus removed. Scientists have found that although all of Dolly's genes within the nucleus of her cells comes from the ewe who supplied the udder cell, the second ewe has contributed the genes of the cell cytoplasm, the part of the cell outside the nucleus.
About 0. The scientists found all of the mitochondria from Dolly and nine other cloned sheep produced by the nuclear-transfer method are derived from the egg cells that received the donated nuclei.
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. Genetics is only part of the story. Even while clones are genetically identical, their phenotypes — the characteristics they express — will be different.
Environment plays a huge role for some characteristics.
0コメント