[Puzzling chromosome behavior in triploid females of Drosophila melanogaster].
Based on a particular formation of the chromocenter and trivalents in triploid Drosophila females, as well as on asynapsis in pericentromeric regions (which is a result of trivalent competition), an explanation for the increased frequency of crossing over and nonrandom segregation of the X chromosomes and autosomes in the first meiotic division is suggested. It is proposed that a delay in pairing of the pericentromeric heterochromatic chromosome regions combined into a single chromocenter leads to the following: (1) formation of the heteroduplex structures (X structures) takes more time and, consequently, their number and the frequency of crossing over in the paired chromosome regions increases; (2) in nonhomologous chromosomes, the chromocentral connections, which normally degrade in prometaphase, are retained to fulfill a function of coorientation during the first meiotic division.
D000818:Animals; D020090:Chromosome Segregation; D002875:Chromosomes; D003434:Crossing Over, Genetic; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D008540:Meiosis; D009865:Oocytes / Q000502:physiology; D011123:Polyploidy; D014960:X Chromosome