A detailed schematic representation of high resolution G-banding patterns was prepared from elongated and finely banded mitotic chromosommes of the mouse. Such chromosomes can be obtained from both animal tissue and cell lines by a simple protocol, facilitating precise demarcation of break points in chromosome rearrangements, as well as aiding in sublocalization of genes. Regions of subbanding homology were observed between human and mouse chromosomal segments known to have conserved gene assignments indicating that, at the cytogenetic level, extensive regions of the mammalian genome may remain intact after 60 million years of species divergence. (Copyright (c) 1986 by the American Association for the Advancement of Science.)