BIOLOGIA	Aspectos biológicos de los animales clónicos
	© Pedro Esponda, 2003  esponda@cib.csic.es

[RESUMEN]ABSTRACT

Clonic animals can be produced by both natural and artificial modes. Natural clonics are those naturally produced, such as univitelin twins. In other mammals, such as the armadillo, clonic reproduction is habitual and up to eight twins can be born. Furthermore, in some invertebrates, female populations are formed exclusively clonically. There are two mechanisms to produce artificial clonics: a) The embryo division, which imitates the method used by nature to create twins, b) Nuclear transplant, which consist in the injection of a nucleus in an egg, which was the procedure used to clone the sheep Dolly in 1997 and by which several clonics (mouse, rabbit, cow, sheep) have been produced so far. The principal purpose to create clonics has been to reproduce transgenic animals (important for biotechnology, biomedicine and pharmacy). Recently, the use of cloning procedures for the production of cell and tissues for xenotransplants has been pointed out. This possibility, which would obviously be applied to humans with therapeutic purposes, has created a great discussion. Actually, the creation of adult human clonics seems very difficult because of the great number of embryos and “mothers” needed. On the other hand, we must think that, despite some few species that naturally use cloning mechanisms, nature has been always inducing the variability as a way to get advantageous characteristics and that favours animal speciation.