Biology
Grade-9
Easy
Question
Which of the following is known as the nucleolus organizer region?
- Primary constrictions
- Secondary constrictions
- Telomere
- Chromomere
Hint:
Secondary constrictions
The correct answer is: Secondary constrictions
Chromosomal satellite’ is the term given to that part of the end of a chromosome that is separated from the rest of the chromosome by a secondary constriction.
The secondary constriction marks the site of a nucleolar organizer region (NOR), a region containing multiple copies of the 18S and 28S ribosomal genes that synthesize ribosomal RNA required by ribosomes. The NOR remains attached to the nucleolus during interphase, and nucleolar remnants remaining on the chromosome may lead the chromatin fiber containing the ribosomal genes to persist as a thin thread at metaphase.
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