Chimaeras and mosaics for dissecting complex mutant phenotypes

Back at the first half of the 1980s, there was no mammalian experimental embryology in Hungary. One of us, AN, took up the challenge of establishing a small group in the field. In the absence of local information, AN and his former colleague, Andras Paldi (AP), used their tourist passport to visit several laboratories in Western Europe and collect information and advice. This is how AN and AP ended up one day sitting in Anne McLaren's office in the MRC Mammalian Development Unit at University College, London. They never forgot her endless enthusiasm and the way she clearly explained the important points of preimplantation embryo manipulation, chimaera making and embryo transfer. As well as the extremely useful suggestions, which were crucial to starting the lab in Hungary, they also took back her deep love for embryo development. They remember her telling them, 'never waste an embryo--there is always another unanswered question it can solve'. Many who have been lucky and experienced Anne's spirit and advice later realized how useful it was to generate 'new' ideas by following the 'not wasting' principle. Our views on chimaeras presented below definitely contain elements which grew out from this principle.