EM studies of female meiosis in wood lemmings with different sex chromosome constitutions.
The chromosomes were studied throughout meiotic prophase by electron microscopy of surface-spread oocytes from one XX, four X*X, and three X*Y female wood lemmings, Myopus schisticolor. The X* chromosome had originated from X by a deletion and an inversion in the short arm. The deletion was confirmed in pachytene cells from X*X females; a D-loop was present in the sex bivalent in 16.8% of the cells, and asynapsis of unequal ends was seen in 9.1% of other cells. At late pachytene the D-loop underwent synaptic adjustment. The breakpoints of the deletion are in G-light bands. No inversion loop was seen, which also is in agreement with Ashley's ('88) hypothesis; at least one of the presumed breakpoints of the inversion is in G-dark chromatin. Various types of synaptic abnormalities, such as nonhomologous pairing (triple pairing, interchange, self-synapsis), univalents, foldbacks, and broken lateral elements, were encountered in all types of female. X*Y females showed a high frequency of abnormal oocytes (70.7%), which significantly exceeded that of X*X (23.1%) and XX (8.1%). Univalents were particularly common in the X*Y females. J. Exp. Zool. 290:504-516, 2001.
Akhverdyan
M
M
Department of Conservation Biology and Genetics, Evolutionary Biology Centre, Uppsala University, SE-75236 Uppsala, Sweden.
Fredga
K
K
D000818:Animals; D003411:Arvicolinae / Q000502:physiology*; D002455:Cell Division / Q000502:physiology; D020090:Chromosome Segregation; D005260:Female; D008540:Meiosis; D008938:Mitosis; D009865:Oocytes / Q000166:cytology / Q000648:ultrastructure; D012730:Sex Chromosomes / Q000648:ultrastructure*; D013573:Synaptonemal Complex; D014960:X Chromosome; D014998:Y Chromosome