What is the Difference Between Chiasmata and Synaptonemal Complex

The key difference between chiasmata and synaptonemal complex is that chiasmata are chromatin structures that attach homologous chromosomes to opposite spindle poles, while synaptonemal complexes are protein structures that mediate synapsis and cross-over.

A chromosome is a thread-like genetic material that consists of genes responsible for the features and characteristics of an organism. A chromosome has two identical strands known as chromatids. During the process of cell division, the chromosomes replicate so that the resultant daughter cells receive a complete set of chromosomes. Homologous chromosomes attach together through structures called chiasmata. During the mediation of the pairing of homologous chromosomes, the synaptonemal complex starts to form.

CONTENTS

1. Overview and Key Difference
2. What is Chiasmata 
3. What is Synaptonemal Complex
4. Similarities – Chiasmata and Synaptonemal Complex
5. Chiasmata vs Synaptonemal Complex in Tabular Form
6. Summary – Chiasmata vs Synaptonemal Complex

What are Chiasmata?

Chiasmata are points of contact between two chromatids that belong to homologous chromosomes. At a chiasma, an exchange of genetic materials takes place between two chromatids, and it is known as chromosomal crossover. Such instances are more frequent in meiosis than in mitosis. When a tetrad splits, the contact point that remains is the chiasmata. It becomes visible during prophase I of meiosis. Sister chromatids form chiasmata between them, which is known as a chi structure. Since their genetic materials are identical, they give rise to identical daughter cells and do not show any change. In mammals, the number of chromosomal arms represents the number of cross-overs, while in humans, only one chiasma is present in a chromosomal arm.

Chiasmata are essential to attach homologous chromosomes to opposite spindle poles, and co-segregation takes place with opposite poles during meiosis I. This process is known as bipolar attachment. The loss of chiasmata leads to improper chromosomal segregation and aneuploidy during anaphase. The point of the cross-over becomes visible as chiasma after the synaptonemal complex dissembles and homologous chromosomes separate from each other.

What is Synaptonemal Complex?

Synaptonemal complex is a protein structure that forms between homologous chromosomes during meiosis and mediates synapsis and recombination during meiosis I in eukaryotes. Synaptonemal complexes usually act as a scaffold, allowing the interaction between chromatids to complete cross-over. The two side structures on either side known as lateral elements connect through proteins called transverse filaments.

Synaptonemal complex develops during the prophase in meiosis I. The synaptonemal complex forms by the pairing of homologous chromosomes and is used to probe the presence of any abnormalities in pairing. The synaptonemal complex shows only a little variation in the structure even though there are protein differences. Synaptonemal complex carries recombination nodules that associate with the central space. These nodules correspond to cross-overs or mature genetic recombination events.

What are the Similarities Between Chiasmata and Synaptonemal Complex?

• Chiasmata and synaptonemal complex are visible in meiosis I.
• Both structures belong to homologous chromosomes.
• Moreover, they take part in the chromosomal crossover during meiosis.

What is the Difference Between Chiasmata and Synaptonemal Complex?

Chiasmata are chromatin structures that attach homologous chromosomes to opposite spindle poles, while synaptonemal complexes are protein structures that mediate synapsis and cross-over. Thus, this is the key difference between chiasmata and synaptonemal complex. Also, chiasmata are cross-shaped structures, while the synaptonemal complex appears as a zipper-like structure. Moreover, chiasmata are composed of DNA and protein, while synaptonemal complex is only composed of proteins.

The below infographic presents the differences between chiasmata and synaptonemal complex in tabular form for side by side comparison.

Summary – Chiasmata vs Synaptonemal Complex

Chiasmata are points of contact between two chromatids that belong to homologous chromosomes. Synaptonemal complex is a protein structure that forms between homologous chromosomes during meiosis, mediates synapsis, and recombination/cross-over. Chiasmata are essential to attach homologous chromosomes to opposite spindle poles, and co-segregation takes place with opposite poles while synaptonemal complexes act as a scaffold, allowing the interaction between chromatids to complete crossing over. So, this summarizes the difference between chiasmata and synaptonemal complex.

Reference:

1. “Chiasmata.” An Overview | ScienceDirect Topics.
2. “Synaptonemal Complex.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Meiosis crossover” By Boumphreyfr – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Synaptonemal complex” By Daniel G. Peterson, Mississippi Genome Exploration Laboratory, Mississippi State University, Mississippi State, Mississippi, United States. – Hey J: What's So Hot about Recombination Hotspots? PLoS Biol 2/6/2004: e190. doi:10.1371/journal.pbio.0020190 (CC BY 2.5) via Commons Wikimedia