What is the Difference Between Homologous Recombination and Non-homologous Recombination

The key difference between homologous recombination and non-homologous recombination is that homologous recombination takes place through strand invasion to produce recombinant chromosomes, while non-homologous recombination takes place through end processing to seal double-stranded breaks. 

Recombination is an important process for genomic evolution and diversification. The process by which damaged DNA is repaired is the mechanism of genetic recombination. Homologous recombination consists of a series of interrelated pathways which help to repair double-stranded DNA breaks and inter-strand crosslinks. Non-homologous recombination is a pathway that is also associated with DNA double-strand repair, especially in higher eukaryotes.

CONTENTS

1. Overview and Key Difference
2. What is Homologous Recombination  
3. What is Non-homologous Recombination
4. Similarities – Homologous Recombination and Non-homologous Recombination
5. Homologous Recombination vs Non-homologous Recombination in Tabular Form
6. Summary – Homologous Recombination vs Non-homologous Recombination

What is Homologous Recombination?

Homologous recombination is a type of genetic recombination that takes place during meiosis. The paired chromosomes from male and female parents align during homologous recombination so that similar DNA sequences from paired chromosomes cross over each other. This is known as strand invasion. Such crossovers result in the shuffling of genetic material, causing genetic variation among offspring. Homologous recombination is mainly used to repair harmful breaks occurring in DNA through a process called homologous recombination repair. Such DNA repair tends to result in non-crossover products, restoring the damaged DNA molecule as it was before the double-strand break.

Homologous recombination is used during horizontal gene transfer to exchange genetic material between various strains of bacteria and viruses. Homologous recombination is conserved among all domains as well as in DNA and RNA viruses. Thus, homologous recombination is nearly a universal biological mechanism. This is strongly associated with increased susceptibility to cancer, gene targeting, and gene therapy. It is essential in cell division in eukaryotes. Homologous recombination repairs DNA damages caused by ionizing radiation or damaging chemicals. In addition to DNA repair, it also helps to produce genetic diversity through meiotic cell division to become specialized gamete cells.

What is Non-Homologous Recombination?

Non-homologous recombination is a pathway that repairs DNA double-strand breaks. It is referred to as non-homologous since the break ends directly ligate without the need for a homologous template. This pathway is usually guided by short DNA sequences called microhomologies. These exist in single-stranded overhangs on the ends of DNA double-strand breaks.

Non-homologous recombination repairs the break accurately when these overhangs are perfectly compatible. Inappropriate non-homologous recombination leads to translocation and telomere fusion in tumour cells. Non-homologous recombination pathway exists in almost all biological systems and is the predominant double-strand break repair pathway in mammals. During the inactivation of this pathway, the double-strand breaks are repaired by a more error-prone pathway. Repairs through this pathway lead to the deletion of DNA sequences between microhomologies. Archaea and bacteria lack a non-homologous pathway. In contrast, eukaryotes utilize a number of proteins during non-homologous recombination pathway. This takes place in steps such as end binding and tethering, end processing, and ligation.

What are the Similarities Between Homologous Recombination and Non-homologous Recombination?

• Homologous and non-homologous recombination are genetic recombinant pathways.
• Both repair double-strand breaks in DNA.
• Recombination takes place between DNA strands during both processes.
• Moreover, they mainly take place in eukaryotes.
• They are important in gene targeting and gene therapy.

What is the Difference Between Homologous Recombination and Non-homologous Recombination?

Homologous recombination takes place through strand invasion to produce recombinant chromosomes, while non-homologous recombination takes place through end processing to seal double-stranded breaks. Thus, this is the key difference between homologous recombination and non-homologous recombination. Also, homologous recombination takes place between long DNA strands while non-homologous recombination is guided by short DNA sequences. Moreover, homologous recombination takes place in eukaryotes, bacteria, and viruses while non-homologous recombination takes place mainly in eukaryotes.

The below infographic presents the differences between homologous recombination and non-homologous recombination in tabular form for side by side comparison.

Summary – Homologous vs Non-homologous Recombination

Homologous recombination is a type of genetic recombination that takes place during meiosis with the need for a template. Meanwhile, non-homologous recombination is a pathway that repairs DNA double-strand breaks. It is referred to as non-homologous since the break ends directly ligate without the need for a homologous template. Moreover, homologous recombination takes place through strand invasion to produce recombinant chromosomes. Whereas, the non-homologous recombination takes place through end processing to seal double-stranded breaks. Besides, homologous recombination takes place between long DNA strands and in eukaryotes, bacteria, and viruses. But, non-homologous recombination is guided by short DNA sequences and happens mainly in eukaryotes. So, this summarizes the difference between homologous recombination and non-homologous recombination.

Reference:

1. “Homologous Recombination.” Genome.gov.
2. “Non-Homologous End Joining.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “HR in meiosis” By Emw – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Non homologous end joining and microhomology mediated end joining” By Cynth3004 at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia