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.' Nucleolus in nucleus remain associated with NOR region of scondary constriction area. In human, number of NOR is equal to number of nucleolus. In human, number of NOR is 10.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). Genes for 5S are present on Chromosome number 1Due to secondary constriction, a knob like structure is formed at the end called as SAT-chromosome.DNA in secondary constriction which form rRNA is called as rDNA. 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.' Nucleolus in nucleus remain associated with NOR region of scondary constriction area. In human, number of NOR is equal to number of nucleolus. In human, number of NOR is 10.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). Genes for 5S are present on Chromosome number 1Due to secondary constriction, a knob like structure is formed at the end called as SAT-chromosome.DNA in secondary constriction which form rRNA is called as rDNA. NOR occurs in SAT (satellite chromosome) chromosomes (13,14,15,21,22).