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Schematic karyogram of a human. Each row is vertically aligned at centromere level. The top of chromosomes 13, 14, 15, 21, & 22 are satellites, with a secondary constriction between the satellite and the centromere.
Secondary constrictions are the constricted or the narrow region found at any point of the chromosome other than that of centromere (primary constriction). The difference between the two constrictions can be noticed during anaphase, as chromosomes can only bend at the site of primary constriction. Secondary constrictions are useful in identifying a chromosome from a set. There are either 0, 1, 2, 3, or 4 secondary constriction sites in a cell at anaphase.
Some parts of these constrictions indicate sites of nucleolus formation and are called "nucleolar organizing regions" (NORs). The nucleolus in the nucleus remains associated with the NOR of the secondary constriction area. In humans, the number of NORs is equal to the number of nucleoli, which is ten. However, not all secondary constrictions are NORs.
The formations of nucleoli takes place around the NOR region.
The secondary constriction also contains the genes for rRNA synthesis (18S rRNA, 5.8S rRNA, and 28S rRNA). Genes for 5S rRNA are present on chromosome 1.
Due to secondary constriction, a knob-like structure is formed at the end called a satellite chromosome (SAT chromosome).
DNA in a secondary constriction which forms rRNA is called rDNA.[clarification needed].
NORs occur in SAT chromosomes (13,14,15,21,22).
and 28 Related for: Secondary constriction information
Secondaryconstrictions are the constricted or the narrow region found at any point of the chromosome other than that of centromere (primary constriction)...
behind the secondaryconstriction, called a satellite, named by Sergei Navashin, in 1912. Later, Heitz (1931) qualified the secondaryconstriction as the...
Constriction ring syndrome (CRS) is a congenital disorder with unknown cause. Because of the unknown cause there are many different, and sometimes incorrect...
the presence of a chromosomal satellite (a segment distal to a secondaryconstriction), the human chromosomes are classified into the following groups:...
mechanism of Raynaud's phenomenon which are reduced blood flow, blood vessel constriction and neurogenic, inflammatory, and immune responses. It is induced by...
late growth stages, these can be preceded by a collar and shallow secondaryconstriction. Weak ribs occurs at late growth stages. Sepkoski, Jack (2002)....
Cornélio MT, Santos K, Soares Filho WD (1997). "Chromosome number and secondaryconstriction variation in 51 accessions of a citrus germplasm bank". Brazilian...
certain arteries in the brain are constricted. Blood flow is blocked by constriction and blood clots (thrombosis). A collateral circulation develops around...
the velum, as in the English "dark" L, [lˠ]. Pharyngealization is a constriction in the throat (pharynx) and is found in the Arabic "emphatic" consonants...
causes an erection. Improper vasoconstriction may also play a role in secondary hypertension.[citation needed] To summarize, vasoconstriction is a physiological...
height and shape of the cell to change. This process is known as apical constriction. The result is a flattening of the differentiating neural plate which...
that are going through it or surround it. Inside the cavernous sinus, constriction of the following cranial nerves (CN) can be found: CN III (oculomotor...
infection properly, the syphilis can progress to the secondary stage.[citation needed] The secondary stages of syphilis persists to be more dangerous to...
inflammatory component, often in response to allergens. In asthma, the constriction of the bronchi can result in difficulty in breathing giving shortness...
karyotype to around 5.5 in pairs 7–13. Pair 10 exhibits an obvious secondaryconstriction. The majority of the autosomes are either metacentric or submetacentric...
vocal tract where its production occurs.: 10 It is a point where a constriction is made between an active and a passive articulator. Active articulators...
400 μm (1/60 of an inch) and have a chrome-orange hue. There is a marked constriction in the front part of the body in the nymph and adult stages. The best...
contrasts with consonants, such as the English "sh" [ʃ], which have a constriction or closure at some point along the vocal tract. In the phonological definition...
and frequency may be indicative of an underlying medical condition. Constriction, asphyxiation – petechiae, especially in the eyes, may also occur when...
or increase. However, depending on the situation, amlodipine inhibits constriction and restores blood flow in coronary arteries as a result of its acting...
to left heart disease (WHO Group II) is completely different in that constriction or damage to the pulmonary blood vessels is not the issue. Instead, the...
colourless, and have one to three cross-walls (septa) with occasional secondaryconstrictions in each cell. They often have a granular surface texture, are slightly...
snake in the family Colubridae. The species subdues its small prey by constriction. It is found throughout the southeastern and central United States. Though...
porosity is less than visual porosity, by an amount that depends on the constriction of holes. Casting porosity is a consequence of one or more of the following:...
century by Wolff, suggested that the aura in migraines is caused by constriction of intracranial vessels (vessels inside the brain), and the headache...
shortening of crown height. Crowns may appear bulbous with prominent constriction at the CEJ. Radiographically, the pulp is small or is totally obliterated...
minutes of standing. It occurs predominantly by delayed (or absent) constriction of the lower body blood vessels, which is normally required to maintain...
have a distinct abdomen that is separated from the cephalothorax by a constriction, and they have three to four pairs of eyes, usually around the margins...
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