Unusual Mechanisms of Chromosome Pairing in Arthropoda
The development of serial sectioning and three-dimensional reconstruction techniques and their application to the study of spermatocyte nuclei at prophase (Wettstein and Sotelo 1967) introduced a new perspective to previous morphological studies. Several authors applied a cytogenetical approach to ultrastructural studies, leading to a better knowledge of meiotic chromosome zones and to a complete analysis of pachytene chromosome complement of several species. The application of these concepts to the study of the ultrastructure of mammalian sex chromosomes allowed the establishment of a structural and behavioural pattern (especially through the extensive work performed by Solari). Both differentially condensed sex chromosomes present axial structures during meiotic prophase and pair their common ends, forming a short SC segment while the free ends vary in their morphological characteristics from species to species. This model is clearly appliable to all but one of the eutherian mammal species studied up to now. Several years ago, we planned in our laboratory the study of a number of invertebrate species which, being representative of different Arthropod groups, could be selected as examples of several types of chromosome mechanisms of sex determination.
KeywordsMeiotic Prophase Diffuse Stage Axial Element Early Pachytene Late Pachytene
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