Chromosomes are thread-like structures that are packed with long DNA molecules, along with histone and nonhistone proteins inside a nucleus. Each chromosome is composed of two chromatid sisters that are joined by a centromere. Centromeres are important structures on a chromosome. They are the sites of attachment of kinetochores that assemble microtubules and spindle fibres for the process of cellular division.
Refer: Structure, Functions and Properties of Chromosomes
The chromosomes are of three different types, based on the number of centromeres they possess. The three types are monocentric, dicentric, and polycentric chromosomes.
Monocentric Chromosomes
The chromosomes that have only one centromere joining the two sister chromatids are known as monocentric chromosomes. They occur commonly in all types of plants and animals.
Based on the position of the centromere, they can be of different types such as acrocentric, telocentric, submetacentric ,and metacentric chromosomes.
Dicentric Chromosomes
Dicentric chromosomes are the ones that have two centromeres in their chromosomes. Translocation and paracentric inversion are two methods that are known to form dicentric chromosomes. When two chromatid segments, each with a centromere attach with each other, they form dicentric chromosomes.
Dicentric chromosomes can be used clinically to study abnormalities in human genomes. They can be used as biomarkers to study genetic syndromes. They also find applications in cytogenetics.
Polycentric Chromosomes
A chromosome featuring multiple centromeres is called polycentric chromosome. They are produced as a result of a chromosomal anomaly such as translocation, deletion or duplication. Cells with such a type of chromosome tend to die because they cannot separate at the anaphase stage. The chromosomes are fragmented, and as a result, the cell dies.
However, polycentric chromosomes are a common occurrence in certain algal species.
Monocentric vs Dicentric vs Polycentric Chromosomes
| Monocentric Chromosomes | Dicentric Chromosomes | Polycentric Chromosomes |
| Description | ||
| Chromosomes with a single centromere are termed as monocentric chromosomes. | Chromosomes with two centromeres are termed dicentric chromosomes. | Chromosomes with multiple centromeres are referred to as polycentric chromosomes. |
| Formation | ||
| They exist naturally in the cells. | They are formed as a result of translocation and paracentric inversion. | They are formed as a result of deletion, duplication and translocation. |
| Number of Centromeres | ||
| 1 | 2 | Multiple |
| Found in | ||
| They are commonly found in plant and animal cells. | They are rarely found in plant and animal cells. | They are a common occurrence in algal species. |
| Clinical Significance | ||
| The centromere acts as a site for the assembly of cell division machinery. | It can be used to study genetic abnormalities in the genome. | No such significance, because the cells tend to die. |
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Also Read:
- Metacentric, Telocentric and Acrocentric Chromosomes
- Who Discovered the Chromosome?
- What is the Difference between Chromosome and Chromatid
Frequently Asked Questions
Why is a dicentric chromosome with two centromeres unstable?
A dicentric chromosome with two centromeres is unstable because there is pulling on both the centromeres on the same chromatid causing DNA breakage.
Are centromere and centrosome the same thing?
No, centromere is a repetitive DNA sequence that joins two chromatids of a chromosome. On the other hand, centrosome is an organelle found in animals that serves as a centre for microtubule assembly.
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