title: Side-by-side pairing of the XY bivalent in spermatocytes and the ubiquity of the H-Y locus.
abstract: The pairing mechanism of the XY bivalent, the possibility of crossing-over between X and Y chromosomes during meiotic prophase, and the location of the H-Y locus are of interest with regard to genetic control mechanisms, male gametogenesis, and testicular organization. A whole-mount electron microscope technique has permitted the study of a large number of mouse and hamster spermatocytes to evaluate the spatial relationship of sex chromosomes and autosomes. X and Y chromosomes showed a transient, extensive side-by-side pairing segment along most of the length of the Y chromosome. This extensive pairing segment may cause genetic exchange between X and Y chromosomes. The finding of a small unpaired paracentromeric region of the Y chromosome could be related to a locus of totally sex-linked gene(s) that determine the development of the testis from the undifferentiated embryonic gonad.
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D006224:Cricetinae; D003434:Crossing Over, Genetic; D005260:Female; D008297:Male; D008540:Meiosis; D008647:Mesocricetus; D051379:Mice; D011418:Prophase; D012730:Sex Chromosomes / Q000648:ultrastructure*; D013090:Spermatocytes / Q000648:ultrastructure*; D013094:Spermatozoa / Q000648:ultrastructure*; D014960:X Chromosome / Q000648:ultrastructure*; D014998:Y Chromosome / Q000648:ultrastructure*