Mr. Koehler et al., CYTOGENETICS OF THE GENUS LEPORINUS (PISCES, ANOSTOMIDAE) .1. KARYOTYPE ANALYSIS, HETEROCHROMATIN DISTRIBUTION AND SEX-CHROMOSOMES, Chromosome research, 5(1), 1997, pp. 12-22
Cytogenetic analyses (Giemsa staining, C-banding, of nucleolus organiz
er regions with base-specific fluorochromes) were performed on the Sou
th American fish species Leporinus friderici, L. obtusidens and L. elo
ngatus. The overall karyotypic structure, position of NORs, as well as
the amount, distribution and composition of constitutive heterochroma
tin were determined. Particular attention was given to the highly diff
erentiated ZZ/ZW sex chromosome system of L. obtusidens and L. elongat
us. Sharing the apparently ancient macroscopic karyotype of Anostomida
e, all three species have 2n=54 meta- or submetacentric chromosomes. N
ORs were found exclusively on chromosome pair 2, which may represent t
he ancestral NOR-bearing chromosome of the anostomid karyotype. Observ
ed differences in the relative position of NORs along chromosome 2 and
variations in the amount and distribution of constitutive heterochrom
atin throughout the karyotype were most probably caused by heterochrom
atin-mediated chromosome rearrangements. Detailed analysis of the morp
hologically similar heteromorphic ZZ/ZW sex chromosomes of L. obtuside
ns and L. elongatus allowed detection of differences in the DNA compos
ition of the largely heterochromatic W chromosomes. However, since the
se and the W chromosomes of three other Leporinus species exhibit homo
logies with respect to their relative size, centromere position and am
ount and distribution of heterochromatin, it is concluded that they ev
olved from the same ancestral W chromosome.