Modification of the technique of chromosome studies in mammalian oocytes

A technique for chromosome study in mouse metaphase II oocytes is presented. The main features are: 1. combined application of hypotonic solution (1.12% sodium citrate) and colchicine 100 micrograms/ml at 37 degrees C for 45-60 min, 2. simultaneous transfer of many or all the oocytes from the hypotonic solution on a slide, 3. mild fixation (methanol: acetic acid: water 5:1:4) for 30 sec. then proper fixation (methanol: acetic acid 3:1), both on the slide, 4. avoiding cooling of oocytes below 22-24 degrees C (room temperature). The technique prevents loss of chromosomes and fragments of oocytes during fixation. The transfer of all oocytes simultaneously on the slide and finding of large stained oocytes are easier in comparison to other techniques. Dispersion of chromosomes within oocytes is suitable for chromosome studies in about 50% of oocytes.