Content area
Full Text
Genetica (2012) 140:307315 DOI 10.1007/s10709-012-9680-7
Molecular cytogenetic characterization of the Amazon River dolphin Inia geoffrensis
Heidi L. Bonifcio Vera M. F. da Silva
Anthony R. Martin Eliana Feldberg
Received: 16 January 2012 / Accepted: 8 September 2012 / Published online: 26 September 2012 Springer Science+Business Media B.V. 2012
Abstract Classical and molecular cytogenetic (18S rDNA, telomeric sequence, and LINE-1 retrotransposon probes) studies were carried out to contribute to an understanding of the organization of repeated DNA elements in the Amazon River dolphin (boto, Inia geoffrensis). Twenty-seven specimens were examined, each presenting 2n = 44 chromosomes, the karyotype formula 12m ? 14sm ? 6st ? 10t ? XX/XY, and fundamental number (FN) = 74. C-positive heterochromatin was observed in terminal and interstitial positions, with the occurrence of polymorphism. Interstitial telomeric sequences were not observed. The nucleolar organizer region (NOR) was located at a single site on a smallest autosomal pair. LINE-1 was preferentially distributed in the euchromatin regions, with the greatest accumulation on the X chromosome. Although the karyotype structure in cetaceans is considered to be conserved, the boto karyotype demonstrated signicant variations in its formula, heterochromatin distribution, and the location of the NOR compared to other cetacean species. These results contribute to knowledge of the chromosome organization in boto and to a better understanding of karyoevolution in cetaceans.
Keywords Boto Heterochromatin polymorphism
FISH LINE-1 retrotransposon 18S rDNA
Introduction
New tools are available for investigating chromosome evolution in eukaryotes, including mapping of repetitive DNA and chromosome banding. Combinations of these approaches have made it possible to identify chromosomal rearrangements, conduct comparative analyses, and to gain insights into phylogenetic relationships and genome organization (Nguyen et al. 2008; Cabral-de-Mello et al. 2010).
Repetitive DNA constitutes a large fraction of the mammalian genome (Acosta et al. 2008). Some sequences are organized in tandem, for example multigenic families such as ribosomal DNA (rDNA) and telomeric sequences, while others are dispersed in the genome as transposable elements (Charlesworth et al. 1994).
In the mammalian genome, the most successful family of transposable elements is the long interspersed nuclear elements (LINE-1) (Graham and Boissinot 2005), an insertional mutagen that can multiply in the genome by retrotransposition (Lee et al. 2010). It provides the enzymatic machinery for retrotransposition of non-autonomous elements of the SINE...