The increasing use of genetically modified mice since their advent 20 years ago amplifies this problem. Genetically modified mice either lack a specific gene or gene-pair (knock-out mice) or carry a piece of foreign DNA integrated into their own chromosomes (transgenic mice), and are used to deduce the functions of particular genes.
El uso cada vez mayor de ratones modificados genéticamente desde que se crearon hace 20 años amplifica este problema.