A cytogenetic study of Diplomystes mesembrinus (Teleostei, Siluriformes, Diplomystidae) with a discussion of chromosome evolution in siluriforms

摘要

The mitotic chromosomes, nucleolus organizer regions (NORs), C-banding pat tern and nuclear DNA content of Diplomystes mesembrinus were studied. The karyotype, with 2n=56 chromosomes (22m+24sm+6st+4a), has a high chromosome arm number (NI: = 102), one chromosome pair with NORs, and a very small amount of heterochromatin. The NOR-bearing arm is entirely heterochromatic and exhibits a marked size polymorphism. The diploid DNA content detected in erythrocyte nuclei of D. mesembrinus was 2.57 +/- 0.15 pgucleus. The chromosome evolution in Siluriformes is discussed on the basis of available cytogenetic data and it is proposed that 2n=56 is synapomorphic for the order. [References: 23]