The centromeric index
(CI) was used to classify the chromosomes according to Levan et al.
The classification of chromosomes, length of the long (1) and short arms (s), arm ratio, centromeric index
(s/1x100), and relative chromosomal length (a chromosome / totalx100) were measured with image analysis systems KAMERAM & Canon A 640 camera.
The best metaphases were photographed and amplified and measured with the help of a 0.02 mm precision caliper to obtain centromeric index
in order to proceed to the construction of the karyotype.
For each chromosome centromeric index
, arm ratio and total length were calculated as described by Levan et al.
The karyotypes were also analyzed by (a) Stebbins (1958) two-way system; (b) Romero Zarco (1986) intra (A1) and inter (A2) chromosomal system; and (c) AI index as proposed by Paszko (2006) which is composed by the chromosome length (CVcl) coefficient of variation and by centromeric index
(CVci) coefficient of variation.
To infer cytotaxonomic relationships within Ostreinae, we constructed ideograms, based on relative length and centromeric index
values, number and location of major ribosomal genes (either by FISH with ITS1 or AgNORs), and C-banding (Fig.
p, short arm; q, long arm; [micron]m, micrometer; d.e, standard deviation; r, proportion of arms; i.c, centromeric index
; d, difference between arms; m, metacentric; sm, submetacentric; t, telocentric; * t, microchromosomes.
The X chromosome shows submetacentric morphology (centromeric index
1.83), constitutes 2.1 % of the diploid set, and exhibits more intensive staining than other chromosomes (i.e., positive heteropycnosis) during some periods of meiotic division.
To avoid any possibility of misclassification of the chromosome type, the index (L/S) was determined for 30 pairs of the chromosomes NO 20 from different individuals, finding that the centromeric index
was always, within the SM range.
farreri consisted of the following chromosome types: three metacentric (m), four submetacentric (sm), seven submetacentric or subtelocentric (sm-st, centromeric index
[+ or -] SD overlaps two categories), four subtelocentric (st), and one subtelocentric or telocentric (st-t) (Table 1).
Idiograms were drawn based on mean centromeric index
and arranged in order of decreasing size.
The centromeric index
was calculates according to Levan et al.