The investigators provide the fertile stud males. The minimum number of males provided is 5 at the age of 8 to 12 weeks. However, the cryopreservation process can be completed sooner if the investigator provides more mice than that. The females used as oocyte donors might be from the inbred or hybrid strains bred by the facility, or any mutant or other strain from an external source. According to the number of available male studs, an equal number of wild type females is superovulated and set up for mating for each day of freezing. The embryos are recovered at the 2-4 and/or morulae cell stage, and at this stage they are frozen in cryo-straws. Embryos are cryopreserved with customised vitrification or the 2-step freezing method. The frozen samples are kept for long term storage in liquid nitrogen tanks.
Our aim is to create a frozen stock of at least 400 embryos per mutant line.