How species differ from each other is a key question in biology. But genetic mapping between species has been challenging, because hybrid crosses are typically sterile. Combining latest stem cell and genomic techniques, the research group has pioneered in vitro
recombination to circumvent breeding and directly cause gene exchanges in cells. In this way they have mapped differences between mouse species within weeks and created mouse embryos carrying hybrid mosaic genomes. By circumventing species barriers that prevent interbreeding this work sheds light on the genetic basis of trait variation.