The chromosomes of Micromys minutus (Rodentia, Murinae). II. Pairing pattern of X and Y chromosomes in meiotic prophase.
Both light and electron microscopy were used to study the pairing behavior of the sex chromosomes of the harvest mouse, Micromys minutus, in surface-spread pachytene spermatocytes. The XY pairing pattern is very exceptional in that the site of synaptic initiation is located interstitially in the short arms of the X and the Y, next to their centromeric regions. From this tiny euchromatic site, synapsis proceeds unidirectionally along the homologous heterochromatic short arms of the X and the Y toward the ends of the chromosomes. After pairing of the short arm is concluded, synapsis begins between the nonhomologous long arms of the X and the Y in the immediate vicinity of the centromeres and progresses unidirectionally toward the end of the long arm of the Y. A synaptic complex develops between the constitutive heterochromatin of the long arm of the Y and the euchromatin of the long arm of the X. Analysis of C-banded and distamycin A/DAPI-stained diakineses revealed a trefoil-like XY bivalent, which was interpreted to be the result of an interstitial chiasma occurring in the paired short arms of the X and the Y. A conspicuous, electron-dense body, about 1 micron in diameter, was found closely associated with the centromeres of the X and the Y in numerous pachytene spermatocytes. A review of the literature showed that comparable XY-associated bodies have been found in only eight other mammals to date.
Schmid
M
M
Institut für Humangenetik, Universität Würzburg, Federal Republic of Germany.
Johannisson
R
R
Haaf
T
T
Neitzel
H
H
D000818:Animals; D002871:Chromosome Banding; D007621:Karyotyping; D008297:Male; D008540:Meiosis; D008854:Microscopy, Electron; D009115:Muridae / Q000235:genetics*; D011418:Prophase; D013090:Spermatocytes / Q000648:ultrastructure*; D014960:X Chromosome / Q000648:ultrastructure; D014998:Y Chromosome / Q000648:ultrastructure