Number and Size of Nucleoli in the Spermatocytes of Chicken and Japanese Quail

Abstract

Nucleoli are the product of nucleolus organizing region activity (NOR) of specific chromosomes. Their basic function is to synthetise ribosomal RNA precursors and promote the maturation and assemblage of preribosomal RNP molecules. Information on rRNA-coding gene activity can be provided by the analysis of the number and size of nucleoli in the prophase of the first meiotic division. The morphology and ultrastructure of a nucleolus depends, among others, on the species and cell growth cycle as well as the physiological and pathological state of an organism. The purpose of this research was to determine the number and size of nucleoli in the spermatocytes of the domestic chicken and the Japanese quail. Diverse numbers and sizes of nucleoli in the cells of the analysed birds were observed. 1-4 nucleoli were identified in chicken cells (1.91 +/- 0.63 on average) and 1-2 in quail cells (1.13 +/- 0.33 on average). For the total of 957 nucleoli observed in Gallus cells, 329 were classified as large and 628 as small. In Coturnix cells, 563 nucleoli were identified (66 large and 497 small ones). An analysis of the numbers and sizes of nucleoli can be performed at the cytogenetic level and serve as an alternative source of information on rRNA encoding gene and nucleolus organising region (NOR) activities.