A C-band Polymorphism of the X Chromosome in Akodon azarae (Rodentia, Cricetidae).

Abstract

Akodon azarae is one of several rodent species in whose populations XY fully fertile females are found. The chromosomes of 83 specimens (40 females, 43 males) from three localities were studied. A high incidence of XY females was observed: 21 of the females presented an XY karyotype. The X chromosome relative length corresponded to 8.2% of the genome, but a significative portion of it consisted of C-positive material, giving to the euchromatic part a relative length of 5.07%, in agreement with the estimated size of the eutherian X. Four C-banding patterns (I-IV) of the X chromosomes were observed, one of them found in only one specimen. The X chromosome of males was type I, and XY females showed an X of type II or III. XX females presented one X of type I and the other of type I, II, III or (in only one animal) of type IV. The significance of this polymorphism with respect to the XY female phenotype is briefly discussed.

Karyotypic Relationship between Akodon azarae and A. boliviensis (Rodentia, Sigmodontinae).

“…In accordance with previous descriptions (Bianchi et al 1971, Ortiz et al 1998, the specimens of A. azarae showed a karyotype composed of 17 telocentric autosome pairs, a small bibrachial one which is characteristic of the genus, a subterminal X and a bibrachial Y that is the smallest chromosome of the karyotype. Only the first pair, the small bibrachial and the sex chromosomes are recognizable in unbanded cells.…”

“…Again, only the first pair, the small bibraquial and the gonosomes can be identified in unbanded metaphases. With respect to C-bands, it has been shown that in A. azarae, centromeric bands can be found in the autosomes, excepting the small biarmed one; the Y chromo- some is heterochromatic, and the X presents several bands that originate a polymorphic pattern (Ortiz et al 1998). In A. boliviensis, on the other hand, the only heterochromatic regions observed are the short arm of the X chromosome and the long arm of the Y (Pinna Senn et al 1993).…”

“…Its species are extensively distributed in South America, and can be found in different habitats through most part of the subcontinent. This genus is cytogenetically very interesting, not only because of its systematic complexity, but also due to the considerable karyotypic variation existent (2n= 10-52), the intraspecific variation concerning the autosomes and the sex chromosomes, and the presence of species with fertile XY females (Barquez et al 1980, Bianchi and Merani 1984, Bianchi et al 1971, 1979a, b, 1993, Fagundes et al 1997, Gallardo 1982, Geise et al 1998, Ortiz et al 1998, Pinna Senn et al 1993, Reig 1987, Silva and YonenagaYassuda 1998, Vitullo et al 1986, Wittouck et al 1995.…”

Characterization of the Chromosomes of Three Species of Akodon (Rodentia, Sigmodontinae) by Means of Fluorochromes Highly Selective for DNA Base Composition.

“…However, the taxonomy and systematics of the genus remain unresolved, mainly due to the great similarity between its species, and thus a comprehensive revision of the genus would be welcome (Diaz et al 1999). This genus is cytogenetically very interesting because of its systematic complexity, its considerable karyotypic diversity (2n =10-52), but, paradoxically, karyotypically indistinguishable species, the existence of intraspecific variation affecting the autosomes and the sex chromosomes, and the presence of species with fertile XY-females (Bianchi et al 1971, 1973, 1979a, b, 1989, 1993, Fagundes et al 1998, Fernandez-Donoso et al 2001, Gallardo 1982, Ortiz et al 1998, Silva and Yonenaga-Yassuda 1998, Vitullo et al 1986, Wittouck et al 1995.…”

“…azarae is one of the species of Akodon in whose populations fertile XY females are present (Bianchi and Contreras 1967, Bianchi et al 1971, 1989, 1993, Espinosa and Vitullo 1996, Ortiz et al 1998, Solari et al 1989. A. molinae and A. dolores share an interesting polymorphism of their first chromosome pair, which can appear as a submetacentric or as 2 subterminal chromosomes, whilst A. dolores exclusively shows Robertsonian polymorphisms of pairs 2 to 5 (Bianchi et al 1973, 1979a, b, Fernandez-Donoso et al 2001, Wittouck et al 1995.…”