stentina, with 6 metacentric and 4 submetacentric chromosome
pairs, revealed a karyotypic formula very similar to that of O.
Notropis Notropis Notropis greenei rubellus tristis Number of specimens examined 3 3 5 Number of metaphases examined 152 145 91 Number of (haploid) NOR chromosomes 1 1 1 NOR chromosome phenotype* D D D *NOR chromosome phenotype (after Gold and Amemiya, 1986; Amemiya and Gold, 1988): D, NOR terminal on the short arm of a medium-sized submetacentric chromosome
A submetacentric chromosome
with an interstitial band midway between the telomeric band and the centromeric band; there were no interstitial bands located on the long arms, although occasionally a tertiary constriction can be found on the long arms of the chromosomes.
The ratio of the total length of metacentric chromosomes to that of the submetacentric chromosomes
was calculated for both the parent species.
The majority of about 89 species reported in the class Bivalvia, exception for Pectinidae and Teredinidae, had mostly metacentric and submetacentric chromosomes
. In the present study, the chromosome number and karyotype of hard clam are similar to the most members of Veneridae, such as Ruditapes philippinarum, R.
corrugata suggests a deletion process of the short arms in some submetacentric chromosome
pairs, originating subtelocentric pairs.
nigra has, beyond the X-autosome fusion, a second one, involving a long acrocentric autosome (the third in size among the medium-sized group), giving rise to a pair of submetacentric chromosomes
that is the largest of the complement.
These specimens have a 2n=24 (NF=48) karyotype (Figure 1e), with 22 metacentric and two submetacentric chromosomes
, and NORs, as detected by Ag-staining (Figure 1f) or FISH with the 18S rDNA probe (Figure 1g), located on the telomeric region of the long arms of the largest metacentric pair.
irradians, 5st + 11t, contained only subtelocentric and telocentric chromosomes and no metacentric or submetacentric chromosomes
Number of submetacentric chromosomes
: with six and eight submetacentrics (0), 10 submetacentrics (1), 12 submetacentrics (2), 14 submetacentrics (3), 16 submetacentrics (4), 18 submetacentrics (5), 20 submetacentrics (6), 22 submetacentrics (7).
The B genome was characterized by two submetacentric chromosomes
; one of which had a small satellite and five median chromosomes.