A range of methods are being used to create genetically modified and cloned animals for research and livestock purposes, and cross-species chimeras for research or to create organs for medical transplants.
Genetically modified animals are created by altering the genes of animal gametes or early embryos, and using those reproductive cells to impregnate an animal. Cloned animals are typically produced with a procedure known as somatic cell nuclear transfer, which involves transferring the nucleus of a body cell from the animal to be “copied” into an egg cell that has had its own nucleus removed. The resulting embryo-like construct can then be triggered to begin developing, and used to initiate a pregnancy. Chimeras are created by combining genetic material from different species, sometimes including humans, into a single embryo.
Many applications of animal biotechnologies are controversial for environmental, health, animal welfare, and social reasons. For example, only a small percentage of cloning attempts produce live offspring and many animal clones are unhealthy; some leading scientists believe that none are “normal.” Human-animal chimeras raise safety concerns about whether new diseases could be transmitted to humans, legal issues about whether such creatures can be patented and owned, and the troubling possibility that they could display human-like behavioral characteristics.