Question

What is centromere? How does the basis of centromere form the basis of classification of chromosomes? Support the answer with a diagram showing the position of centromere on different types of chromosomes?

Answer 1

Hint: A closely packed structure and a very specific portion of the chromosome, and during cell division it has a very important role. It is responsible for the movement during mitosis and meiosis of the replicated chromosomes into the two daughter cells.

Complete answer:

A centromere is a chromosome constricted region which separates it into a short arm and a long arm. The chromosomes first multiply during cell division, so that each daughter cell receives a full set of chromosomes. The chromosome consists of two identical sister chromatids that are connected at the centromere during DNA replication.

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 signalling to the cell cycle machinery when all chromosomes have proper attachments to the spindle, so that cell division is safe to proceed to completion The centromere is the point on a chromosome where, during cell division, mitotic spindle fibres bind to pull sister chromatids apart.

The chromosomes are primarily categorised on the basis of centromere positions:
> Telocentric: The centromere of the telocentric chromosome is positioned at the terminal end of the chromosome. Consequently, a telocentric chromosome only has one arm. Telomeres can stretch from both ends of the chromosome; their form during anaphase is similar to the letter "i." The typical house mouse karyotype, for example, only has telocentric chromosomes.

> Acrocentric: They are found at the end of a chromosome in these centromeres. Five acrocentric chromosomes are part of the human genome: 13, 14, 15, 21, 22, and the Y chromosome is also acrocentric.

> Submetacentric: They are generally L-shaped and the chromosome is assumed to be submetacentric if the arms' lengths are unequal.

> Metacentric: these are X-shaped chromosomes, the centre of which is the centromere, such that the two chromosome arms are almost identical. A chromosome is metacentric if the length of its two arms is approximately equal. Five chromosomes are found metacentric in the standard human karyotype: chromosomes 1, 3, 16, 19, and 20.

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