An improved method for chromosome preparations from preimplantation mammalian embryos, oocytes or isolated blastomeres.

A method is described for making chromosome preparation from mammalian oocytes or preimplantation embryo, with or without the zona pellucida, or from isolated blastomeres. It is more robust and requires less skill and experience than previous techniques, yet chromosome structure is well preserved and very high quality preparations can be made. The method, which involves use of cold hypotonic solution and very cold fixative, reduces turbulence and allows even single blastomeres to be located and handled with relative case, while the duration of hypotonic treatment becomes noncritical. The softening solution recommended contains no lactic acid and hence does not harm the chromosomes.