The key difference between monocentric dicentric and polycentric chromosomes is that monocentric chromosomes have one centromere, and dicentric chromosomes have two centromeres while polycentric chromosomes have more than two centromeres.
Chromosomes are thread-like structures composed of DNA and histone proteins. Chromatids, centromeres, chromomeres and telomeres are distinct regions of a chromosome. The centromere is the visible point of constriction in the chromosome which joins sister chromatids together. The centromere is extremely important since it is the chromosomal locus where the kinetochore is formed, and microtubules attach during cell division. Based on the number of centromeres, chromosomes are different types. Monocentric chromosomes have only one centromere. Dicentric chromosomes have two centromeres while polycentric chromosomes have more than two centromeres. Acentric chromosomes, on the other hand, do not have a centromere.
CONTENTS
1. Overview and Key Difference
2. What are Monocentric Chromosomes
3. What are Dicentric Chromosomes
4. What are Polycentric Chromosomes
5. Side by Side Comparison – Monocentric vs Dicentric vs Polycentric Chromosomes in Tabular Form
6. Summary
What are Monocentric Chromosomes?
Monocentric chromosomes have only one centromere. They are the most abundant type of chromosomes. This type of chromosome is present in many organisms, especially in plants and animals. Based on the position of the centromere, there are several types of monocentric chromosomes.
Figure 01: Monocentric Chromosome
Monocentric chromosome can be known as acrocentric when the centromere is positioned at the end of the chromosome. It can be called metacentric when the centromere is present at the center of the chromosome. In telecentric chromosomes, the centromere is present in the telomere region.
What are Dicentric Chromosomes?
Dicentric chromosomes are chromosomes that have two centromeres. These two centromeres are present in the arms of the chromosome. They are a type of abnormal chromosomes. Dicentric chromosomes are formed when two chromosomal segments with a centromere in each join end to end. When fusion, they lose their acentric chromosomal segments, leading to the formation of dicentric chromosomes. Therefore, dicentric chromosomes are formed as a result of genome rearrangements. The formation can occur between any two chromosomes.
Figure 02: Dicentric Chromosome
The stability of the dicentric chromosome differs. They are typically unstable. A dicentric chromosome which is naturally stable can be found in rice. Sometime dicentric chromosomes are present in the human population. However, they achieve stability through the inactivation of one centromere. There is only one functional centromere; hence, they successfully segregate during mitosis and meiosis. However, dicentric chromosomes in humans can be associated with birth defects and reproductive abnormalities.
What are Polycentric Chromosomes?
Polycentric chromosomes are the chromosomes that have multiple centromeres or more than two centromeres. The formation of polycentric chromosomes takes place due to chromosomal aberrations such as deletion, duplication, or translocation. Polycentric chromosomes usually cause cell death. Polycentric chromosomes are unable to move into opposite poles during cell division. Once they fail to move, they become fragmented, causing cell death. However, in certain organisms such as algae especially in Spirogyra, polycentric chromosomes appear normally.
What is the Difference Between Monocentric Dicentric and Polycentric Chromosomes?
The key difference between monocentric dicentric and polycentric chromosomes is the number of centromeres present in each type. Monocentric chromosomes have a single centromere while dicentric chromosomes have two centromers and polycentric chromosomes have more than two centromeres. Monocentric chromosomes are the most abundant in organisms, while dicentric and polycentric are abnormal types of chromosomes.
Below infographic tabulates the differences between monocentric dicentric and polycentric chromosomes.
Summary – Monocentric Dicentric vs Polycentric Chromosomes
The number of centromeres present on a chromosome differs among chromosomes. Acentric, monocentric, dicentric and polycentric chromosomes are such types. Monocentric chromosomes have a single centromere. Dicentric chromosomes have two centromeres while polycentric chromosomes have multiple centromeres (more than two centromeres). Both dicentric and polycentric chromosomes are abnormal types of chromosomes which result in different disease conditions and abnormalities. Thus, this is the summary of the difference between monocentric dicentric and polycentric chromosomes.
Reference:
1. “Types of Chromosomes.” Biology Wise, 15 June 2011, Available here.
2. Stimpson, Kaitlin M, et al. “Dicentric Chromosomes: Unique Models to Study Centromere Function and Inactivation.” Chromosome Research : an International Journal on the Molecular, Supramolecular and Evolutionary Aspects of Chromosome Biology, U.S. National Library of Medicine, July 2012, Available here.
Image Courtesy:
1. “Paracentric inversion dicentric chromosome formation” By Acp095 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Chromosome” By !File:Chromosome-upright.pngOriginal version: Magnus Manske, this version with upright chromosome: User:Dietzel65Vector: derivative work Tryphon – Own work based on: Chromosome-upright.png (CC BY-SA 3.0) via Commons Wikimedia