Several chromosomes from the mouse bivariate flow karyotype have been sorted, identified, and cloned. Peaks representing the mouse Y, 19, 18, 1,2,3, and X chromosomes have been sorted and identified. This new information has been published. The resulting libraries are being used to identify the mouse X and Y chromosomes contained in hybrid cell lines and for assaying transgenic mice that contain a desired mutation or "knock-out" in the germline.