[Activity of the embryonal genome of mink during diapause (cytogenetic analysis): number of cells and cell nucleus size in blastocysts or various size and age].

The number of cells and the morphology and size of the nuclei of these cells in diapausal mink embryos were investigated. Growth of blastocysts from 0.25 to 1.2 mm in diameter in the complete absence of classical mitoses is accompanied by an increase in the average number of cells per embryo from between 100 and 150 to 2000, respectively; diameters of cell nuclei vary from 6 to 19 and from 6 to 53 micron, respectively. Some giant nuclei exhibit morphological signs of polyteny. In all nuclei, the number of active (silver-stained) nucleoli does not exceed that of nucleolar organizers in the mink diploid genome. The obtained results, combined with data from the literature, allow the inference that polytenization of trophoblast cells followed by cryptic segregation of genomes provides the key mechanism for rapid growth of diapausal blastocysts.