Starbuck II a calf that was cloned

Sheep egg being injected with an embryonic cell during sheep cloning

Pelagic jellyfish

Closed anemone

Megan and Morag, two Welsh mountain sheep cloned at the Roslin Institute in Scotland

Several reasons have been given for continuing work on human cloning: it could offer help for people who can't have children; it could make it possible to reproduce a child that has died or, even, a celebrity. Imagine an Einstein clone. However, would that really be Einstein? Human cloning could also make available stem cells that might rejuvenate and repair our bodies.

The cloning of animals lets us duplicate exceptional characteristics, such as those of a bull who has great reproductive value, or of a transgenic animal. One day we may be able to clone pets. Some people say that through cloning we can then produce pets that are easy to handle, and reduce the risk that they will be abandoned.

Dr. Lawrence Smith and Starbuck II

Dr. Lawrence Smith and three cloned calves

Pandas

Dodo bird

Some people see cloning as a way to remedy the problem of endangered species, and to reproduce those that have already disappeared. In order to use cloning to recreate a species, you would need to:

• obtain intact DNA, which is difficult;

• establish a community of animals that could reproduce, which is difficult if you are starting off with only a few, and especially if they are all of one sex;

• ensure the genetic diversity of the species, which is difficult to do with just one individual specimen;

• find a natural habitat for this species, otherwise they would be condemned to live in a zoo.

Mammoth tooth (Pleistocene)

A piece of amber-containing insects (Pleistocene)

Cloning an animal 

Cloning is the ultimate phase in creating an animal with a desired trait. It follows the same path as selective breeding, artificial insemination, egg transplantation and in vitro fertilization. In genetics, cloning means creation of genetically identical animals (mammals) by means of nuclear transfer. In nuclear transfer, the chromosomes of an unfertilized oocyte (egg) are removed (enucleation) and a nucleus from a mature (diploid) cell is placed into the egg (see figure). Note that no fertilization takes place and it is the presence of a diploid nucleus inside an egg, which initiates cleavage divisions. Cloning, when it becomes more practical to do, has the potential to make copies of a bred line of cattle, sheep or other economically important animals without having to do artificial selection. Another application is to clone genetically modified pigs to use their organs for xenotransplantation. The modification is required to prevent immune response. The cloned animal may not be fully identical to the animal who donated the nucleus. This is because of some epigenetic phenomena (methylation patterns) and cytoplasmic (extra-nuclear) inheritance. It appears that cloned mammals usually have a collection of disorders called large offspring syndrome (LOS). Most cloned mammals so far have also developed deformities and arthritis (like Dolly). There is still a long way to go to optimize the conditions of cloning if it will ever be a common practice.