Kretschmer, R., et al. 141

J. Biotec. Biodivers. v. 5, N.2: pp. 140-147 May 2014

INTRODUCTION

The karyotype description of all species is crucial to map the genome. In addition, a karyotype providesvaluable information about genetic characteristics of an animal or cell line (Masabanda et al. 2004) and for phylogenetic and evolutionary analysis as well (Pieczarka and Nagamachi 2004). The birds karyotype is characterized by having a high diploid number (2n=78-80), a few pairs of macrochromosomes and many pairs of microchromosomes (Christidis 1990). The difficulty in distinguishing chromosomes, due to the presence of microchromosomes, does not occur for most of other classes in which chromosomes can be distinguished easily by techniques of classical or molecular cytogenetic (Masabanda et al. 2004). Due to these complexities, few works are conducted inbirds cytogenetic, for instance, less than 14% of the Brazilian birds are known through cytogenetic studies (Santos and Gunski 2006). Thus, more information is necessary to identify chromosomal rearrangements that had occurred during the speciation in order to understand the karyotype evolution of this class.

The precursor in birds cytogenetic studies was Guyer (1900), which examined the spermatogenesis of doves and hybrids. In Brazil, pioneering work was done by Aguiar, in 1965. Since the 70th decade methodology has been improved with the advent of classical cytogenetic techniques, such as banding with barium hydroxid and silver staining. The use of these techniques allowed a significant increase in detection, interpretation and understanding of chromosomal rearrangements and also reveal important aspects of constitutive heterochromatin and nucleolus organizer regions (NOR) (Correia et al. 2009). Recently, analyzes with fluorescence in situ hybridization (FISH) have been used as a complement of conventional methods used to identify chromosomal rearrangements (De Oliveira et al. 2005). However, due to the high cost and complexity in performing FISH techniques, prior application of classical cytogenetic analysis and chromosome banding,in order to choose the

right chromosomal probes, contribute significantly to obtain satisfactory results (De Oliveira et al. 2006).

The chromosomal characterization by classical and molecular cytogenetics has revealed important information about the evolutionary state of different groups of birds in relation to the ancestor of this class. For example, the presence of only one chromosome pair bearing 18/28S rDNA sequences in species of the Cathartidae family ( Gymnogyps californianus , Sarcoramphus papa , Cathartes aura and Cathartes burrovianus ) is considered as a plesiomorphic state (primitive state) in this family (Raudsepp et al. 2002 Tagliarini et al. 2009). This assumption is based at the observation that NOR-bearing chromosomes correspond to pair 16 in chicken (Ladjali- Mohammedi et al. 1999). Species of Paleognathae birds ( Pterocnemia pennata , Dromaius novaehollandiae , Casuarius casuarius , Struthio camelus and Rhea americana ) also show only one pair bearing 18S-28S rDNA (Nishida-Umehara et al. 2007). The Mimida e family comprises more than 30 species, where only Mimus saturninus (Lucca 1974) and Toxostomarufum (Jovanovic 1969) have been described cytogenetically. In these studies chromosome banding was not performed, being described only the diploid number and morphology of the macrochromosomes for both species and the Z sex chromosome for Toxostoma rufum . Considering this context, our aim was to perform a cytogenetic analysis of the species Mimus saturninus through classical cytogenetic methods including identification of constitutive heterochromatic regions and nucleolus organizer regions.

MATERIAL AND METHODS

One female and one male chick of Chalk- browed Mockingbird ( Mimus saturninus )were sampled for this study. They were collected at the Experimental Farm of the Federal University of Pampa, located in Dom Pedrito, Rio Grande do Sul State (RS), Brazil (Fig. 1).