For each chromosome centromeric index, arm ratio and total length were calculated as described by Levan et al.
The arm ratio and the centromeric index ranged between 1-[infinity]and 0-50 respectively.
Relative length (100 x chromosome length/total haploid length) and centromeric index (100 x length of short arm/total chromosome length) were calculated.
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.
Arm ratio (AR) and centromeric index
(CI) was determined according to Levan et al.
(Ci) was calculated by dividing 100 times the length of the short arm by the total chromosome length.
Additionally, the chromosomal measurements were used to determine both relative lengths and centromeric index
according to Levan et al.
Chromosomes were classified according to their centromeric index
and arranged by decreasing size (Levan et al.
Measurements were used to determine relative lengths of chromosomes (length of the chromosome pair / total complement length x 100) and centromeric index
(length of short arm / total length of the chromosome x 100) of each chromosome.
A total of 356 chromosomes were randomly measured and their centromeric index
was calculated (100 x length of short arm/total chromosome length).
The relative length of chromosomes 1 to 18 was not different between the species, but 5 of their chromosomes (numbers 4, 7, 9, 11, & 18) were significantly different in relative lengths of short and long arm and in centromeric index
, differences that can be explained by pericentric inversions.
The measurements were used for determiner relative lengths of chromosomes and centromeric index
(100 x length of short arm/total chromosome length).