NHGRI logo
Centromere_hero

​Centromere

updated: May 19, 2022

Definition

The centromere appears as a constricted region of a chromosome and plays a key role in helping the cell divide up its DNA during division (mitosis and meiosis). Specifically, it is the region where the cell’s spindle fibers attach. Following attachment of the spindle fibers to the centromere, the two identical sister chromatids that make up the replicated chromosome are pulled to opposite sides of the dividing cell, such that the two resulting daughter cells end up with identical DNA.

 Centromere


Narration

The centromere is a very specific part of the chromosome. When you look at the chromosomes, there's a part that is not always right in the middle, but it's somewhere between one-third and two-thirds of the way down the chromosome. It's called the centromere. That's the part where the cell's chromosomes are constricted, and they're a little bit tighter, and it almost looks like a little ball in the middle of two sticks. The centromere is what separates the chromosome into what we call, for human chromosomes, the P and Q arm. And these P and Q arms are a part of what we use when we do cytogenetics to say how many chromosomes are present in a cell and what chromosome number they are. That's based on the banding pattern of the cell, but a lot of that is based on how big the P arm is relative to the Q arm. So it's always an important consideration for us to know where the centromere is. That's visually how we use it for some genetic tests, but it's also important that the centromere has a very important function during cell division. During cell division, this is the place where the chromosomes, when they're undergoing replication, that they're held together so that the chromosomes don't lose their sister chromatid during the cell division process.