Abstract
The nucleolar organizers have been localized in the Japanese quail oocyte at pachytene and diplotene stages using hybridization in situ with rRNA. Autoradiography reveals that 8 microchromosomes, forming 4 bivalents at pachytene, contain ribosomal cistrons. The silver grains are located on the microchromosomes euchrpmatic segment, near the centromeric heterochromatin inserted in a chromocenter. This localization coincides with that of the nucleolar fibrillar center as revealed by electron microscopy. At advanced diplotene the silver grains, whose number is increased, are located over the central area of the nucleolus. This situation corresponds to that of the fibrillar centers which multiply at advanced diplotene and move to the central part of the nucleolus. Comparison of pachytene and diplotene grain counts suggests that moderate amplification of the ribosomal cistrons might take place during oogenesis in the quail.
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