Question

Secondary constriction II of the chromosome is concerned with the
(a)Synthesis of rRNA
(b)Synthesis of tRNA
(c)Synthesis of mRNA
(d)All of the above

Answer 1

Hint: Secondary constrictions are the constricted or the narrow region found at any point of the chromosome other than that of the centromere, also known as primary constriction.

Complete answer:
Secondary constriction II of the chromosome is generally concerned with the synthesis of rRNA (ribosomal nucleic acid), which is a ribozyme. Ribosomal RNA (rRNA), a molecule in cells that forms part of the protein-synthesizing organelle known as a ribosome and that is exported to the cytoplasm to help translate the information in messenger RNA (mRNA) into protein, during protein synthesis. The secondary constriction also contains the genes for rRNA synthesis. The difference between the primary and the secondary constrictions can be noticed during the anaphase, as chromosomes can only bend at the site of primary constriction.

Additional Information: -In 1969, Herbert Lubs discovered secondary constriction on the bottom end of the long arm of the X chromosome.
-‘Chromosomal satellite’ is the term given to that part of the end of the chromosome that is separated from the rest of the chromosome by a secondary constriction.
-Secondary constrictions are associated with the nucleolus during interphase of cell division and take part in the reorganization of the nucleolus at the end of the cell division.
-Secondary constrictions are useful in identifying a chromosome from a set of chromosomes.

So, the correct answer is, ‘Synthesis of rRNA.’

Note: The secondary constriction marks the site of a nucleolar organizer region (NOR) (a chromosomal region crucial for the formation of nucleolus), containing multiple copies of the 18S and 28S ribosomal genes that synthesize ribosomal RNA required by ribosomes.