A centromere is a constricted region of DNA or a structure in a chromosome that plays an essential role in the segregation of chromosomes during the process of the cell cycle in eukaryotic cells. It is the site of the duplicated chromosome around which the kinetochore is present to hold together the pair of sister chromatids. The primary role of the centromere is to serve as the kinetochore assembly site, a highly complex multi-protein structure responsible for the actual chromosome segregation events, i.e., binding microtubules and signaling to the cell cycle machinery when all chromosomes have proper attachments to the spindle, so that cell division is safe to proceed to completion.

Centromeres can be defined as the compressed region or a part of elongated chromosomes. They are densely packed with the heterogeneous domain capped by the trilaminar kinetochore, and the DNA of the centromeres is normally in a heterochromatin state, which is required for the attachment of sister chromatids mediated by the cohesin complex and also for the separation during anaphase.

The position of the centromere on the chromosome forms the basis of classification of chromosomes. Chromosomes are divided into four types based on the position of the centromere. These types are:

• Metacentric chromosome: The chromosomes in which the centromere is present in the middle and divides the chromosome into two equal arms.
• Sub-metacentric chromosome: The chromosome in which the centromere is slightly away from the middle region. In this, one arm is slightly longer than the other.
• Acrocentric chromosome: The chromosome in which the centromere is located close to one of the terminal ends. In this, one arm is extremely long and the other is extremely short.
• Telocentric chromosome: The chromosome in which the centromere is located at one of the terminal ends.

During mitosis and meiosis in eukaryotic cells, centromeres play an important role in proper chromosome segregation. They also assist in the adhesion and separation of sister chromatids, microtubule attachment, chromosome movement, heterochromatin establishment, and regulation of mitotic control points.