Question

What is the use of NOR in secondary constriction of a chromosome?

Answer 1

Explanation:

Primary constriction is present in all chromosomes . Secondary constriction is seen at the chromosome in addition to primary constriction/centromere and it is not present in all chromosomes. Secondary constriction is also known as nucleolar organiser region(NOR) involved in the formation of nucleolus.

Answer 2

Nucleolus organiser regions are chromosomal regions crucial for the formation of the nucleolus. In humans, the NORs are located on the short arms of the acrocentric chromosomes 13, 14, 15, 21 and 22, the genes RNR1, RNR2, RNR3, RNR4, and RNR5 respectively. These regions code for 5.8S, 18S, and 28S ribosomal RNA.