C-banding and non-homologous associations in Gyrllus argentinus.

Abstract

A comparative study of C-banded mitotic and meiotic chromosomes of Gryllus argentinus (Gryllidae) is reported. Improved cytological procedures were followed to establish karyotypes and to detect C-segments. Twenty-eight autosomes plus a sexual system XX, XO were found. Terminal C-heterochromatin in both arms and paracentric segments were detected in most of the chromosomes of the complement. Microdensitometric tracings confirmed the distribution of C-banded segments. Manifold connections through condensed terminal chromomeres were observed at pachytene occurring between two or more bivalents during meiosis. These heterologous associations involved the whole karyotype. End-to-end pachytene associations reacted intensely to the C-procedure. C-segments detected at diakinesis allowed the measurement of the centromere indices of bivalents which resulted in a more precise identification of given chromosome pairs. The relationship of the presence of terminal heterochromatin in mitotic chromosomes, the end-to-end associations through C-segments, the attachment of pachytene filaments to the nuclear membrane and their molecular implications is discussed.