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NOR variability in diploid and triploid forms of the amazon molly Poecilia formosa as shown by silver nitrate and Chromomycin A₃ staining

Pedro Manoel Galetti Junior^I; Ellen Marie Rasch^II

^IDepartamento de Genética e Evolução, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brasil. Send correspondence to P.M.G.J.
^IIDepartment of Biophysics, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614-0421 USA

ABSTRACT

Karyotypes for the diploid, gynogenetic Amazon molly fish, Poecilia formosa (2n=46), and its related trihybrid (3n=69) from the Soto la Marina drainage baisin of northeastern Mexico were obtained after short-term kidney cultures and conventional Giemsa staining. Characteristic patterns were established for sites of nucleolar regions (NORs) as identified by silver (Ag) staining and use of the GC- specific fluorochrome Chromomycin (CMA₃). Diploid females consistently showed two NOR-bearing sites. One on the short anus of the largest chromosome and another on the short arms of a small chromosome. Rarely, NOR sites were detected on the short arm of a medium-sized chromosome. Four NOR-bearing chromosomes were routinely detected by Ag- and CMA₃-staining of the triploid chromosome set. These involved one among the largest chromosomes, two medium-sized and a small chromosome. Both diploid and the triploid karyotype showed variability in numbers and staining intensities of NOR sites both between and within individual specimens. Nucleolar frequencies for interphase nuclei from the same kidney cell preparations also showed intra- and interindividual variation, confinning observations on metaphase chromosomes.

Keywords: diploid forms; triploid forms; amazon molly; Poecilia formosa; silver nitrate; Chromomycin A₃.

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