The key difference between micronucleus and macronucleus is that micronucleus is the smaller nucleus that contains the germline genome of the ciliate protozoans while macronucleus is the largest nucleus, containing the somatic genome of ciliate protozoans.
Nuclear dimorphism is the phenomenon of having two different types of nuclei within the same cell. It is a special characteristic present in protozoan ciliates and some foraminifera. These two nuclei are the macronucleus and micronucleus. They contain separate genomes. The macronucleus is the larger one that controls the metabolism of the ciliate protozoa while micronucleus is the smaller one that carries out reproductive functions and generates the macronucleus.
CONTENTS
1. Overview and Key Difference
2. What is Micronucleus
3. What is Macronucleus
4. Similarities Between Micronucleus and Macronucleus
5. Side by Side Comparison – Micronucleus vs Macronucleus in Tabular Form
6. Summary
What is Micronucleus?
Micronucleus is the smaller nucleus out of the two nuclei seen in ciliate protozoans. It contains the germline genetic material of the organism. Hence, it controls the reproductive functions of the organism.
Figure 01: Nuclear Dimorphism
Moreover, these organisms cannot reproduce without micronucleus. Thus, micronucleus is responsible for the genetic reorganization that occurs during conjugation or cross-fertilization. Not only that, but micronucleus also gives rises to the macronucleus. However, the genome of micronucleus is transcriptionally silent. In addition to these, micronucleus contains a comparatively small amount of DNA.
What is Macronucleus?
The macronucleus is the larger nucleus present in ciliate protozoa. It contains somatic genome that has heredity information of the organism. Compared to micronucleus, macronucleus consists of a higher amount of DNA in hundreds to thousands of chromosomes.
Figure 02: Macronucleus
DNA in macronucleus controls the metabolism of the organism. Therefore, it is the centre of metabolic activities of the organism. In fact, macronucleus is responsible for the normal functioning of the cell. Thus, it is the non-reproductive nucleus of ciliate protozoa. Moreover, macronucleus is ellipsoidal in shape, and it is active in transcription. Macronucleus disintegrates during conjugation. But, it reforms from the micronucleus by karyogamy.
What are the Similarities Between Micronucleus and Macronucleus?
- Ciliate protozoans have both micronucleus and macronucleus.
- Both are present within the same cytoplasm.
- And, they have separate genomes.
- Hence, they both code for hereditary information of the organism.
- Thus, both nuclei are equally important for the survival of the organism.
- Further, they control separate cellular processes.
- Most importantly, the micronucleus gives rise to the macronucleus.
What is the Difference Between Micronucleus and Macronucleus?
Ciliates have two nuclei as micronucleus and macronucleus. Micronucleus is the smaller nucleus and the reproductive nucleus. In contrast, macronucleus is the larger one and the non-reproductive nucleus. So, this is the key difference between micronucleus and macronucleus. Micronucleus genome is diploid while macronucleus genome is polyploidy. Moreover, micronucleus contains a small amount of DNA, while macronucleus contains a large amount of DNA. Therefore, this is also a difference between micronucleus and macronucleus.
The following infographic summarizes the difference between micronucleus and macronucleus.
Summary – Micronucleus vs Macronucleus
Ciliates are single-celled eukaryotic organisms that show nuclear dimorphism. They have a micronucleus and a macronucleus. Micronucleus is the reproductive nucleus that contains the germline genome essential for reproduction. In contrast, macronucleus is the non-reproductive nucleus that contains somatic genome essential for all the metabolic and normal functioning of the organism. Furthermore, macronucleus has a comparatively large amount of DNA compared to micronucleus. So, this summarizes the difference between micronucleus and macronucleus.
Reference:
1. “What Is a Paramecium?” LiveScience, Purch, Available here.
2. “Nuclear Dimorphism.” Wikipedia, Wikimedia Foundation, 31 May 2019, Available here.
Image Courtesy:
1. “Ciliate” By Ali Zifan – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Gastronauta clatratus – 400x – Macronucleus & Micronucleus” By Picturepest (CC BY 2.0) via Flickr