On page 1086, Kuroiwa et al. describe a chromosome-cloning system that can handle large segments of genomic DNA. They cloned large fragments of human chromosomes into a mitotically stable human minichromosome using Cre/LoxP-mediated translocation and telomere-directed truncation of the chromosome fragments in a homologous recombination-proficient cell line. Using this approach, a minichromosome containing a 10 Mb fragment of chromosome 22 was introduced and stably maintained in various cell lines, including ES cells and in mice. The human genes present on the insert were functionally expressed in mice.