Secondary constriction
Encyclopedia
Secondary constriction is seen at the chromosome
in addition to primary constriction/centromere
. Chromosome can bend only at the site of primary constriction during Anaphase
. 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 indicates sites of nucleolus formation and so they are called "Nucleolar Organizing Region." (Anaphase is part of cell division)
The formations of nucleolus takes place around the NOR region.
The secondary constriction also contains the genes for rRNA synthesis (18 S, 5.8 S, 28 S)
NOR occurs in SAT (satellite chromosome
) chromosomes (13,14,15,21,22)
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
in addition to primary constriction/centromere
Centromere
A centromere is a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come closest in contact. It is involved in cell division as the point of mitotic spindle attachment...
. Chromosome can bend only at the site of primary constriction during Anaphase
Anaphase
Anaphase, from the ancient Greek ἀνά and φάσις , is the stage of mitosis or meiosis when chromosomes move to opposite poles of the cell....
. 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
Anaphase
Anaphase, from the ancient Greek ἀνά and φάσις , is the stage of mitosis or meiosis when chromosomes move to opposite poles of the cell....
.
Some parts of these constrictions indicates sites of nucleolus formation and so they are called "Nucleolar Organizing Region." (Anaphase is part of cell division)
The formations of nucleolus takes place around the NOR region.
The secondary constriction also contains the genes for rRNA synthesis (18 S, 5.8 S, 28 S)
NOR occurs in SAT (satellite chromosome
Satellite chromosome
The part of chromosome beyond the nuclear organiser is very short and appears like sphere .The Satellite Chromosome is the chromosome which has a bulge on the telomeric end and SAT stands for Sine Acid thymonucleinicosince the chromosome on staining show relative deficiency of DNA in the nuclear...
) chromosomes (13,14,15,21,22)
External links
- "Karyomorphological Studies of Species in Taxodiaceae " - METLA
- "Physical locations of 5S and 18S-25S rDNA in Asian and American diploid Hordeum species with the I genome" - Heredity
- "Evolutionary aspects of the ZZ/ZW sex chromosome system in the Characidae fish, genus Triportheus. A monophyletic state and NOR location on the W chromosome" - Heredity
- "Evolutionary implications of permanent odd polyploidy in the stable sexual, pentaploid of Rosa canina L" - Heredity
- "Molecular characterization of the secondary constriction region (qh) of human chromosome 9 with pericentric inversion" - Journal of Cell Science