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The karyotype of Philodryas chamissonis (Colubridae). Identification of nucleolar organizer region (nor) and sex chromosomes by banding methods

R. Moreno^I; J. Navarro^I; P. Iturra^I; A. Veloso M.^II

^IDepartamento de Biología Celular y Genética, Facultad de Medicina, Universidad de Chile, Casilla 70061-7, Santiago, Chile. Send correspondence to P.I.
^IIDepartamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Santiago, Chile

ABSTRACT

The karyotype, the localization of nucleolar organizer region (NOR) and the sex chromosomes of the snake Philodryas chamissonis are described. P. chamissonis has a diploid number 2n = 36 (16 M + 20 m). Pair 2 is the silver-stained NOR carrier. In P. chamissonis, the hetero-gametic sex is the female, the ZW pair is isomorphic, and the W-chromosome is totally C-band positive. With C-banding and quinacrine mustard the interphase nucleus of female specimens shows Wchromatin. The W-heterochromatinization could be the first step in the W-chromosome differentiation in Colubridae. Comparison of the karyotypes of Philodryas species studied, thus far suggests that in P. chamissonis both the W-chromosome heterochromatinization and different NOR location could be a state derived from an ancestor widely distributed in South America.

Keywords: karyotype; Philodryas chamissonis identification; chromosomes.

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