Mammalian chimaeras / Anne McLaren.

  • Anne McLaren
Date:
[1976]
Catalogue details
    11/168 (page 1)
    1 What is a chimaera? A chimaera is a composite animal. The Chimaera of Homeric legend had the body of a she-goat, the head of a lion, and the tail of a serpent. Many other combinations are described in the literature of antiquity: the six-limbed centaur, half man, half horse; the harpy, a bird of prey with the head and breasts of a woman; the griffon, with eagle's head and legs, and the body of a lion; the beast of the Apocalypse, like a seven-headed leopard with the mouths of a lion and the feet of a bear; the Apocalyptic locusts, horse-shaped with men's faces, women's hair, lions' teeth and scorpions' tails. All bear witness to the ambition of Man to combine the outstanding qualities of dif¬ ferent animals into a single creature of surpassing power. Sexual hybridiza¬ tion is at best a chancy method for this purpose ; it may take several genera¬ tions, the results are unpredictable and it can only be used within a species. Biology as well as mythology provides examples of strange and often inti¬ mate associations between different species. Alga and fungus form a partner¬ ship so close that we refer to it by a single name, 'lichen'; the hermit crab collects stinging sea anemones to guard its shell; the sea slug {Aeolis pilata) accumulates nematocysts from the hydroid that it eats, and positions them in its epidermis as a defence. Even some subcellular organelles, like chloro- plasts and mitochondria, are now thought to have originated as independent organisms existing in symbiotic relationship to the host cell. Some definitions Today, 'chimaera' is used to describe any composite animal or plant in which the different cell populations are derived from more than one fertilized egg, or the union of more than two gametes. Such a situation can arise in various ways. For convenience, Ford (1969) has distinguished between 'secondary chimaerism', where tissues are combined from two or more adult individuals, or from embryos after the period of organogenesis has begun, and 'primary chimaerism', where the genetically different cell populations co-exist from a very early stage of embryogenesis, even from fertilization. Secondary chimaeras can be formed by grafting or transplantation of tissues, for example kidney grafting, skin grafting or blood transfusion, or can arise spontaneously, by transfer of cells in mammals between mother