Chromosomes

• A single human cell has about 2 m long thread of DNA distributed among its 46 (23 pairs) chromosomes.
• Every chromosome has a primary constriction (centromere) on the sides of which disc shaped structures called kinetochores are present.
• Based on the position of the centromere, chromosomes are 4 types.
• o Metacentric chromosome: It has middle centromere forming two equal arms of the chromosome.
• o Sub-metacentric chromosome: It has centromere nearer to one end of the chromosome resulting into one shorter arm and one longer arm.
• o Acrocentric chromosome: Centromere is situated close to its end forming one extremely short and one very long arm.
• o Telocentric chromosome: It has a terminal centromere.
• Some chromosomes have non-staining secondary constrictions at a constant location. It is called satellite.