secondary constriction


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sec·on·dar·y con·stric·tion

a subsidiary narrowing of the chromosome associated in some cases with satellites, for example, the short arms of acrocentric autosomes.
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Presence or absence of secondary constriction -0,31 0,11 0,00 0,23 0,12 4.
crassifolia have secondary constrictions on the long arm of the submetacentric (sm) and subtelocentric (t) chromosome pairs.
In the seven species studied chromosome 3 was the only one carrying a secondary constriction associated with a satellite segment on the long arm (Figures 2 and 3).
All accessions posses' satellites (SAT chromosome) a secondary constriction connected to the long arm near centromeric region (Table 2; Fig.
The interstitial region positively stained with [CMA.sub.3] fluorochrome on the fourth pair of chromosomes was observed in all 3 Atta species; a secondary constriction was also visible, indicating that this GC rich heterochromatic region probably corresponds to the nucleolus organizer region (NOR).
Ogle control slides showed the expected six NOR rDNA hybridization sites (Jellen et al., 1994), the A rrhenatherum accessions had four major hybridization sites on somatic metaphase preparations at the location of the secondary constriction (Fig.
In pair 5, along with the polymorphism a lighter region was observed, that may represent a secondary constriction at the end of the chromosome (Figs.
The varieties displayed two chromosome pairs with secondary constriction (SC) associated with a satellite segment (Sat) visible in metaphase after Giemsa staining and three pairs of chromosomes with Ag-NOR banding (Figures 2D and 2E) seeing that one pair showed a preeminent silver impregnation, followed by one other with a smaller impregnation and by another with a small dot of impregnation.
The majority of the chromosomes did not display differentiated areas along their length aside from the centromeric region and visualization of secondary constrictions in the accessions of one species.
On the basis of size and position of the primary and secondary constrictions, five types of chromosomes A, B, C, D and E were identified in the four species, although the species differed from one another in chromosome types and/or copy number.