Reproductive cloning is expensive and highly inefficient. More than 90 — Cloning

"Lets say that one in a thousand cells were nevertheless viable, practical issues come into play. Given that we have an efficiency of 1% cloning for livestock species and if only one in a thousand cells are viable then around 100,000 cells would need to be transferred," it said."

"Several attempts at cloning exotic or endangered species have received widespread publicity (e.g. Gaur (Bos gaurus), Banteng (Bos javanicus) and Bucardo (Capra pyrenaica pyrenaica)). The distinguishing feature of these examples is that they employed trans-species cloning (Fig. 2⇓). In these instances, the oocyte cytoplasm being used to create embryos was derived from common domesticated species (Bos taurus (cow) or Capra hircus (goat)), while the cell nucleus was from the species of interest. Trans-species clones inevitably differ from either of the parental species in their nucleo-cytoplasmic characteristics. At the very least, mitochondria inherited from the recipient oocyte would have a major influence over functions, such as muscle development and physiology, that depend on mitochondrial gene expression. Animals resulting from these trans-specific cloning efforts would be scientifically valuable for their insights into the functional relationships involved in nucleo-mitochondria dialogue, but would not be directly useful for supporting the endangered populations."

"SNCT is a widely used cloning technique whereby a cell nucleus containing the genetic information of the individual to be cloned is inserted into a living egg that has had its own nucleus removed. It has been used successfully in laboratory animals as well as farm animals. However, until now, scientists hadnt been able to overcome the limitations of SNCT that resulted in low success rates and restricted the number of times mammals could be recloned. Attempts at recloning cats, pigs and mice more than two to six times had failed. "One possible explanation for this limit on the number of recloning attempts is an accumulation of genetic or epigenetic abnormalities over successive generations," explains Dr. Wakayama."

"Populations with low numbers of individuals possess minimal genetic variation. It is therefore desirable to avoid further losses of diversity. A subsequent generation resulting from natural breeding or artificial insemination (AI) would contain some, but not all, of the genetic variability of its parents. Losses would occur if any of the individuals failed to breed, a strong possibility with small populations. If cloning was guaranteed to be 100% successful, a good strategy might be to clone every individual (not impossible if the population size is only 9–18), then allow the offspring to mature and breed naturally. The probability of losing genetic diversity would then be reduced, especially if each parent gave rise to more than two identical copies of itself. Thus, an interesting and novel theoretical principle in animal conservation emerges, where individuals are effectively induced to reproduce asexually, somewhat like plants, thereby improving the long-term fitness of the species through the retention of genetic diversity."

"Current success rates with nuclear transfer in mammals are very low (less than 0.1–5% of reconstructed embryos result in a live birth (Di Berardino 2001, Wakayama & Yanagimachi 2001). Therefore, between 20 and 1000 nuclear transfers would need to be performed to achieve one viable offspring."

"A prominent biologist Lee Silver, once said that biology would be forever defined as BD and AD: before Dolly and after Dolly. Such is the enormity of the findings of the Roslin Institute, where not only was Dolly the sheep created, but her predecessors Tracy, Megan and Morag. These animals are important in terms of their significance to science and the ethical issues that their creation raises."