Solution:

Primary constriction present in a chromosome is called the centromere.

Centromere holds two chromatids of a chromosome.

Based on the position of the centromere, the chromosomes can be classified into four types:

• Metacentric has middle centromere forming two equal arms of the chromosomes.
• Submetacentric chromosomes feature centromeres that are somewhat offset from the chromosome centre, resulting in one shorter and one longer arm.
• Acrocentric chromosomes have a centromere near the end, resulting in one extremely short and one extremely long arm.
• The telocentric chromosome has a terminal centromere.