Robertsonian rearrangements in the reef fish Chromis (Perciformes, Pomacentridae) involving chromosomes bearing 5s rRNA genes

ABSTRACT

Cytogenetic studies were done on three Pomacentridae species of the genus Chromis. The karyotype of C. multilineata consisted of 48 acrocentric chromosomes (FN = 48), C. insolata had 2n = 46-47 (3-4M+6SM+36-38A; FN = 56) and C. flavicauda had 2n = 39 (9M+6SM+24A; FN = 54). Robertsonian polymorphisms were detected in C. insolata and C. flavicauda. All three species had small heterochromatic blocks restricted to centromeric regions. Nucleolar organizer regions (NORs) were detected in the telomeric position of a medium acrocentric chromosome pair in C. multilineata and in non-homologous chromosomes in both C. flavicauda and C. insolata. FISH with a telomeric probe detected no internal telomeric sequences in C. flavicauda and C. insolata. 5S rRNA genes were observed in a pericentromeric region of two large metacentric chromosome pairs in C. flavicauda and two large acrocentric pairs in C. insolata. The karyotype structure and the number and location of the 5S rDNA loci in these two species indicated that the 5S rRNA-bearing acrocentric chromosomes were directly involved in the origin of the polymorphisms observed. These data reinforce the idea that Robertsonian rearrangements have been involved in molding the karyotype in the subfamily Chrominae