Cloning in Animals
Natural Animal Cloning in Invertebrates
- Some animals such as starfish can regenerate entire animals from a fragment if the original is damaged.
- Flatworms and sponges split apart to form new identical animals as part of the normal reproductive process.
- Hydra, a genus of small freshwater animals, produce buds which eventually separate to become individual clones of the parent.
- Some female insects can produce offspring without mating, however further research shows that there is some mutation between the mothers an daughters, suggesting they are not true clones.
- Monozygotic twins are clones of eachother formed from the early separation of an embryo into to embryos. The cause of this is unknown. Incidence varies between species.
- Some female amphibians and reptiles can produce offspring without a male, however this usually results in male offscpring so they are not true clones.
- Some invertebrates are easy to artificially clone - liquidising a sponge or chopping up a starfish will result in many animals regenerating from the fragments.
- It is harder to produce vertebrate, particularly mammalian clones.
- Works on the same principles as the formation of identical twins.
- Each cell in an embryo is totipotent, and has the potential to form any cell in the organism, and can therefore develop into a whole organism.
- An embryo is split more than twice, sometimes into individual cells, producing multiple offspring.
Somatic Cell Nuclear Transfer
- Instead of an embryo, an adult animal can be cloned by taking the nucleus from a somatic (body) cell and putting it into an enucleated cell.
- The process was used to successfully clone the first adult mammal, Dolly the Sheep, in 1996.
- There have been problems in animals cloned by SCNT; Dolly the Sheep had to be put down at 6 years old suffering from signs of premature ageing - arthritis and lung disease.
- However, the process has since been improved, reducing the risk of premature ageing. One Japanese team produced 581 clones of 1 donor mouse over 25 generations, all with normal life spans.
- SCNT can be used in pharming, the production of animal clones which have been genetically engineered, such as cows with therepeutic human hormones in their milk, or to produce human organs for transplant.
- Twinning enables high-yielding livestock to produce many more offspring than normal.
- SCNT enables GM embryos to be replicated and develop, giving many embryos from one engineering procudure.
- SCNT enables scientists to clone specific animals for example pets or racehorses.
- SCNT has the potential to allow endangered species to make a comeback, or to even revive an extinct species.
- SCNT is very inefficient as it usually requires many eggs to successfully produced a cloned offspring.
- Many cloned embryos fail to develop, result in miscarriages or are malformed.
- Many cloned animals have shortened life spans.
- There are religious, ethical and moral concerns.
- Scientists have produced primate clones by artificial twinning, but there is significant difficulty in performing SCNT in primates.
- It is suggested that the proximity of the spindle fibres required for cell division are very close to the nucles, so are damaged in nuclear extraction.
- Also, there is less margin for error in the stage of the embryo's development and the state of primate reproductive organs than in other animals.
- Although in recent years scientists have produced primate embryonic stem cells via SCNT, there is strict laws preventing the cloning of humans.
- However a modified version of SCNT has the potential to produce adult embryonic stem cells which could be used to grow organs for transplant, specific for an individul so they would not trigger an immune response.