| Sumario: | In Calomys musculinus (Rodentia, Cricetidae) the meiosis was studied. Diffuse stage was described with conventional and special techniques, and its chronological location was certainty determined through histological sections.Analysing the distribution and frequency of chiasmata a process of terminalisation was detected from diplotene up to metaphase I. Studying separately the decrease of the mean of interstitial chiasmata (ich), the increase of the mean of terminal associations (ta), and the development of the relationship ta/tch (terminal associations/total chiasmata number) between diplotene-diakinesis and between diakinesis-metaphase I, significant differences were founded.Sequential events of pairing of the XY pair through the formation of their synaptonemal complex in pachytene at O.M. were analyzed. Data obtained allowed to consider the association between X and Y chromosomes as achiasmatic. © 1988, Japan Mendel Society, International Society of Cytology. All rights reserved.
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