Files No:34 Chimeras, Hybrids
Total Page：16
File Type：pdf, Size：1020Kb
files no:34 www.cmf.org.uk chimeras, hybrids By Calum MacKellar and ‘cybrids’ In biotechnology it is now scientists created the world’s first sheep- This reluctance to involve human possible to combine elements goat chimera by fusing a sheep embryo cells and embryos is also found in between organisms of and a goat embryo. The resulting ‘geep’ European documents such as Article consisted of goat cells and sheep cells. 13 of the Council of Europe’s European different species. It is also Externally this combination was obvious, Convention on Human Rights and possible to create cloned as the skin that grew from the sheep Biomedicine, which prohibits any action animals using parts of embryo was woolly, while the areas of skin that aims to modify the human genome eggs from one species and that originated from goat cells bore hair. 3 in a way that will be passed on to future generations. In effect this would ban any nuclear genetic material from The potential power of inter-species genetic technologies applied at a very another. It is even possible combinations became clearer with a series early embryonic stage of life. European to create novel organisms via of experiments conducted in the late policy makers are clearly anxious interspecies combinations 1990s. In these, small sections of brains about the technology, though the UK from quail embryos were transplanted of gametes. Should such government has not so far signed up to into the developing brains of chickens. procedures ever be permissible this convention. between animal species? If When they hatched, the resulting chickens exhibited quail-like vocal trills and head In his January 2006 State of the Union so, should we ever combine bobs, showing that the transplanted parts address, American President George human beings with animals? of the brain were not only incorporated W Bush expressed his position when into the brain, but that such mixing of he slipped in a small but significant Early in 2007 a UK parliamentary tissues could allow complex behaviours to comment that announced his intention committee met to discuss the be transferred between species. 4 to ban human-animal hybrids: ‘A technological and ethical issues hopeful society has institutions of surrounding any possible mixing together The next step for many scientists is to start science and medicine that do not cut of human and animal species. They sat combining human and nonhuman cells. ethical corners, and that recognize the as a response to proposed legislation The immediate objective is not to generate matchless value of every life. Tonight I which, if enacted, would have banned beings that are fully grown half-humans, ask you to pass legislation to prohibit such work. After effective lobbying but to create a source of stem cells that the most egregious abuses of medical from scientists and other associated could potentially be used in research and research: human cloning in all its interest groups, the committee decided therapy. Initial requests for permission forms, creating or implanting embryos in favour of the creation and limited use to perform this work envisage that any for experiments, creating human- of human-nonhuman hybrids, chimeras embryo created by mixing human and 1 animal hybrids, and buying, selling, or and ‘cybrids’. nonhuman cells would not be allowed to patenting human embryos. Human life develop beyond the 14-day stage. The interest in mixing species is neither is a gift from our Creator - and that gift new, nor is it confined to the realms of myth Political landscape should never be discarded, devalued or or fiction. True, many ancient cultures told This push to develop the combining of put up for sale.’ 6 stories and built statues of entities such as human and nonhuman cells has come This File will examine what is currently human-lion sphinxes and winged horses, from technological developments since possible, and what is envisioned for the but the natural mixing of animals has the 1990 legislation. Anxiety about this near future. By drawing on Christian occurred for centuries. A mule, for example, new possibility can however be seen principles it will ask whether any starts life when a male donkey mates with in a 2001 UK report from the Home form of species mixing is ethically a female horse (a cross between a female Office’s Animal Procedures Committee, justified, particularly where one of the donkey and male horse is less common, and which recommended that ‘No licences components is human. called a hinney). The gametes (sperm and should be issued for the production of egg) fuse and the resulting embryo develops embryo aggregation chimeras, especially What’s been done so far into a healthy animal. Though normally not cross-species chimeras between One complication is that there are infertile, there are even occasional reports of humans and other animals, nor of hybrids various ways of deliberately mixing two mules giving birth. 2 which involve a significant degree of species of animal (see box). Each process But in recent years, research has raised hybridisation between animals of very produces a different outcome and raises a host of new possibilities. In 1984 dissimilar kinds’. 5 different issues. CMF file number 34 hybrids hybrids CMF file number 34 Genes from humans in bacteria Defining terms 100 trillion micro-organisms that live that we should prevent future ethical At the simplest end, there are the many primarily on our skin and in our guts. dilemmas by forbidding anyone from chimera hybrid examples of genes harvested from the One paper estimates that humans trying to create an animal that may to An organism made up of cells that come An organism created by combining eggs 15 human genome and placed inside from two genetically distinct individuals. and sperm cells of different species, so that carry more than 500 different species some extent exhibit human capacities. all of its cells contain a mixture of both of micro-organism, and that together bacteria. These transgenic bacteria have This can occur when embryos from two Biblical views of humanity different species are brought together in components. Human-animal hybrids can this means we carry 100 times as many huge medical and commercial potential. potentially be created when:9,10 One way to address the ethical issues early development, and the two sets of cells 12 For example, most insulin is now genes as are found in our ‘own’ cells. merge. In a chimera, each set of cells - a human egg is fertilised by nonhuman sperm incurred by creating human-animal produced from E. coli with the insulin contains components from only one species. - a nonhuman egg is fertilised by human sperm A further argument used against mixtures is to see in what way the gene from a human inserted amongst An example of this is the so-called ‘geep’ mixing individuals is that it will violate resulting creatures would show other genes. These bacteria consequently that was created by combining two A hybrid has two parents of embryos, one from a goat, one from a sheep. different species their genetic uniqueness. That, again, is diminution of features commonly held by produce an individual human protein, It is interesting to note that the geep not as clear as it might seem, because Christians to be important characteristics but are far from bearing any distinctively genetic inheritance would come from the consequently had four parents. ‘cybrid’ same-species chimeras are probably of human beings. human characteristics. Artificial chimeras, nucleus donor. However, considerable (a cytoplasmic hybrid) quite frequent in nature. Some will such as the geep, have four parents information stored in proteins and other Image of God Genes from humans in mice An organism that, like hybrids, has cells components of the egg’s cytoplasm would occur when two embryos fuse as they that all contain components from two also be present, at least in the early embryo, A critical feature all Christians agree on Moving up in scale, there are also many grow in the womb (see box), but other different species. This time, however, the and would most probably influence is that God created human beings to be thousands of strains of mice that have naturally occurring chimera situation is more complex. development. ‘microchimeras’ are created when cells Not all chimeras have four parents. Egg from another in his image and likeness.16 There is less A ‘cybrid’ would be created when nuclear species - without had sizable pieces of genetic code that Human-human chimeras often occur quite from the fetus and placenta break off genetic material from one species was nucleus, but some agreement on the exact meaning of those originated from the human genome naturally. This can happen when two genes and information during pregnancy and birth and enter placed inside an egg from another species. Complete nucleus carrying proteins in separately fertilised embryos growing from one species cytoplasm terms, but most Christians agree it at least spliced into their genes. Many of these In the case of a human-nonhuman ‘cybrid’ the mother’s blood stream. Colonies of side-by-side in the womb merge into one. A implies that humans are in some sense this could be human material placed in a are used in cancer and pharmaceutical variant of this is when a single cell these cells may persist for decades, and nonhuman egg with its nucleus removed, or special and distinct from other parts of experiences a significant genetic change, research as experimental animals that vice versa. on occasions these cells have found such as the loss of a chromosome, but creation. mimic human disease. In terms of each their way across the placentas in future carries on growing.