A centromere is a primary constriction present on every chromosome (visible only in dividing cells). On the sides of the centromere, disc-shaped structures called kinetochores are present. The centromere holds the two chromatids of a chromosome together.

The position of the centromere on a chromosome serves as the basis for classification of chromosomes into four distinct types. This classification depends on where the centromere is located along the length of the chromosome, which determines the relative lengths of the chromosome arms.

The four types of chromosomes based on centromere position are: (i) Metacentric chromosome has middle centromere forming two equal arms of the chromosome. (ii) Sub-metacentric chromosome has centromere slightly away from the middle resulting in one shorter arm and one longer arm. (iii) Acrocentric chromosome has centromere situated close to its end forming one extremely short and one very long arm. (iv) Telocentric chromosome has a terminal centromere.

The diagram shows the position of centromere on different types of chromosomes: the metacentric chromosome appears with centromere in the middle creating equal arms; the sub-metacentric shows centromere slightly off-center creating unequal arms; the acrocentric shows centromere near the end with extremely short and very long arms; and the telocentric shows centromere at the terminal position.