Question

Nucleolar organizer region is found in - (A) Primary Construction (C) Satellite region (B) Secondary Construction (D) Telomere region​

Answer 1

answer : (b)

Explanation: Option A: A chromosome consists of two identical halves, the chromatids which are held together at one point called centromere. The centromere appears as an arrow region called the primary constriction of the chromosome. Primary constriction present between long and short arms.

Option B: Nucleolar organizer is a narrow constriction in the short arm of a few chromosomes. The nucleolar organizer also is known as secondary constriction.

Option C: In the chromosome, there is no tertiary constriction.

Option D: Two cylindrical structures present in a centromere called centrioles, which are surrounded by a cloud of amorphous pericentriolar material called controllers or kinoplasm. These two centrioles called diplosomes are localized in the centrosome at right angles to each other. A centriole possesses a whorl of nine evenly spaced peripheral fibrils of tubulin. It is absent in the center. Therefore, the arrangement is called a 9+0.

So, the correct option is (B).