Macro- and microchromosomes B in females of Astyanax scabripinnis (Pisces, Characidae)

Abstract

Cytogenetic analysis of two populations of Astyanax scabripinnis from the Yukatan stream (Ivai river basin) and from the Agua do Rancho river (Parana basin) revealed the presence of extra chromosomes of 2 differrnt types. The population from the Yukatan stream presented a diploid number of 2n = 50 (3M, 15SM, 2ST and 5A) and a large metacentric B macrochromosome similar in size to the first in the complement in 100% of the cells analyzed (2n = 51) in 31% of the females. The C-banding pattern of this chromosome was partially heterochromatic. The population from the Agua do Rancho river presented a diploid number of 2n = 50 (3M, 14SM. 8A) and a B microchromosome in 32% of the females analyzed, with a range of 0-2 chromosomes per metaphase. These chromosomes were found to be fully heterochromatic when submitted to C banding. Both populations presented extra chromosomes exclusively found in females. Aspects related to the morphology of these B chromosomes and a hypothesis for their origin are discussed.