centromere - Function, The centromeric sequence, Inheritance, Centromeric aberrations

The point on a chromosome, usually a constriction, by which it is attached to the spindle during the division of the cell nucleus. It orchestrates the division of the chromosome into its two daughter chromosomes.

The centromere is a region of chromosomes with a special sequence and structure.

Function

A centromere functions in sister chromatid adhesion, kinetochore formation, pairing of homologous chromosomes and is involved in the control of gene expression.

A centromere is the region where sister chromatids join in the double chromosomal structure during mitosis, prophase and metaphase. The centromere is also where kinetochore formation takes place: proteins bind on the centromeres that form an anchor point for the spindle formation required for the pull of chromosomes toward the centrioles during the anaphase and telophase of mitosis.

The centromeric sequence

In most eukaryotes, the centromere has no defined DNA sequence. However, in budding yeasts the centromere region is relatively small (about 200 bp DNA) and contains two highly conserved DNA sequences that serve as binding sites for essential kinetochore proteins.

Inheritance

Epigenetic inheritance plays a major role in specifying the centromere in most organisms. The daughter chromosomes will assemble centromeres in the same place as the parent chromosome, independent of sequence. The presence of CENP-A is believed to be important for the assembly of the kinetochore on the centromere and may play a role in the epigenetic inheritance of the centromere site. In nematodes such as Caenorhabditis elegans, some plants, and the insect orders Lepidoptera and Hemiptera, chromosomes are "holocentric", indicating that there is not a primary site of microtubule attachments or a primary constriction, and a "diffuse" kinetochore assembles along the entire length of the chromosome.

Centromeric aberrations

In rare cases in humans, neocentromeres can form at new sites on the chromosome. This must be coupled with the inactivation of the previous centromere since chromosomes with two functional centromeres (Dicentric chromosome) will result in chromosome breakage during mitosis.