Reproductive Cloning

Reproductive cloning is the production of a genetically identical copy, a clone of an organism. Dolly- the sheep, produced in 1996 was the first clone of an adult animal, but several other species have been cloned since, including dogs and cats.

The most common method of cloning adult animals is somatic cell nuclear transfer. First the nucleus is removed from an egg's cell, then a somatic cell such as a skin cell is taken from the animal to be cloned. The nucleus containing chromosomal DNA is removed and injected into the egg. The egg is stimulated to divide by chemical or electrical treatment, and forms an embryo, which is implanted into the uterus of an adult female, where it continues to develop until birth.

The resulting clone has identical chromosomal DNA to the original animal, but the mitochondrial DNA is often different since the mitochondria come from the cytoplasm of the egg, usually from a different individual.

Also phenotypic differences between the clone and the original can occur due to environmental and epigenetic factors during development. Just as identical twins are slightly different from each other, despite having the same DNA.