Difference Between Centromere and Chromomere

The main difference between centromere and chromomere is that the centromere is the condensed part of the chromosome, which links the two sister chromatids whereas the chromomere is linearly arranged chromatin granules along the length of the chromosomes. Furthermore, centromere occurs during the interphase of the cell cycle where the DNA replication takes place while chromomere is visible during the prophase of both mitosis and meiosis.

Centromere and chromomere are two structures of a chromosome, which occur during different stages of the cell cycle.

Key Areas Covered

1. What is Centromere
     – Definition, Structure, Function
2. What is Chromomere
     – Definition, Structure, Function
3. What are the Similarities Between Centromere and Chromomere
     – Outline of Common Features
4. What is the Difference Between Centromere and Chromomere
     – Comparison of Key Differences

Key Terms

Centromere, Chromatin, Chromomere, Chromosome, Location of Genes, Idiomere, Sister Chromatid, Spindle Microtubules

What is a Centromere

A centromere is the central region of a chromosome made up of highly condensed DNA. The main function of a centromere is to hold the two sister chromatids together. Sister chromatids form after DNA replication in the interphase. The linkage of two sister chromatids occurs through a cohesion complex. Centromere also provides sites for the attachment of spindle microtubules through kinetochores. Kinetochores are the protein complexes that link centromere to the spindle microtubules.

Figure 1: Centromere

The two types of centromeres are point centromeres and regional centromeres. Point centromeres are the locations to which spindle microtubules are attached. On the other hand, regional centromeres are the DNA sequences that determine the location of spindle microtubule attachment.

Centromere divides the chromosome into two arms as long arm or q arm and short arm or p arm. Based on the position of the centromere, we can identify several types of chromosomes. Below given are the types of chromosomes.

• Metacentric chromosomes – Equal lengths in both p and q arms;
• Submetacentric chromosomes – p and q arms are fairly unequal in lengths;
• Acrocentric chromosomes – q arm is longer than the p arm;
• Telocentric chromosomes – The centromere located at the terminal end of the chromosome.

What is Chromomere

Chromomere is a tightly coiled chromatin thread (chromonemata) found in a chromosome. It is also known as idiomere. A series of chromomeres occur in a chromosome, and they can be observed under a microscope when stained with nuclear dyes. Chromomeres are clearly visible during the prophase of the mitosis and meiosis. They are made up of condensed DNA. 95% of the chromosome condenses, forming chromomeres while the remaining 5% occurs in between the chromomeres. The very large chromomeres formed in plants are called nodules. The conjugation of the homologous chromomeres of the replicated chromosomes forms giant polytene chromosomes. The pattern of the disks of these chromosomes marks the loci of certain genes. 

Figure 2: Chromomeres in Drosophila Polytene Chromosomes

The pattern of the formation of chromomeres is unique to the chromosome; hence the shape, size, and number of chromomeres depend on the chromosome. Chromomeres are the functional units of a chromosome in modern cytogenetics. Thus, the formation of chromomeres is a key mechanism of gene regulation.

Similarities Between Centromere and Chromomere

• Centromere and chromomere are two structures of the chromosome.
• Both are made up of condensed chromatin.

Difference Between Centromere and Chromomere

Definition

Centromere refers to a region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division while chromomere refers to one of the small bead-shaped and heavily staining masses of coiled chromatin that has a linear arrangement along the chromosome.

Significance

The centromere is a result of DNA replication, which occurs in the interphase while chromomere is visible during the prophase of both mitosis and meiosis.

Number

Monocentric organisms contain a single centromere per chromosome, and holocentric organisms contain more than one centromere per chromosome while a large number of chromomeres occur throughout the chromosome.

Location

Centromere occurs in the middle of the chromosome or on an arm while chromomeres occur along the whole chromosome.

Function

The function of the centromere is to hold two sister chromatids together and provide sites for the attachment of spindle microtubules through kinetochore while that of chromomeric maps is to give the exact location of genes on a chromosome.

Conclusion 

A centromere is a structural unit on the chromosome which aids in the attachment of spindle microtubules during cell division. Chromomere is a tightly coiled chromatin thread (chromonemata) found in a chromosome. The main difference between centromere and chromomere is their structure and function. 

Reference:

1. “Centromere – Definition, Function and Types.” Biology Dictionary, Biology Dictionary, 28 Apr. 2017, Available Here
2. “Chromomere.” The Free Dictionary, Farlex, Available Here

Image Courtesy:

1. “Figure 10 02 03” By CNX OpenStax – http://cnx.org/contents/[email protected]:rZudN6XP@2/Introduction (CC BY 4.0) via Commons Wikimedia 
2. “Drosophila polytene chromosomes 2” By J. Albert Vallunen (User:albval) – Own work (CC BY-SA 2.5) via Commons Wikimedia