Figure 1. A schematic diagram showing rotation matings. Obtaining the appropriate number of gametes from each treated male is important for mutagenesis. To obtain enough gametes before ENU-treated males succumb to illness (in particular, the commonly used C57BL/6J strain is susceptible to the development of T-cell lymphoma), rotation matings are advised. Place each male into a new cage with one or two females each week for 6- wk, depending upon how many gametes are needed from each male. If two females are used, a pregnant female can be placed into a separate cage for bearing her litter, if required by the institutional animal protocol. The rotation breeding strategy also improves efficiency of weaning and mutation recovery. Females are shown in white; males are shown in black.