Secondary constriction

Secondary constriction can be found at a chromosome in addition to primary constriction/centromere. Chromosomes 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 indicate sites of nucleolus formation and are called "Nucleolar Organizing Regions." 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)there are 3types of satallites:-

1 terasrteronmus 2 ectospricuus 3 amnaliracritus

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