The key difference between homologous recombination and site-specific recombination is that in homologous recombination, genetic material is exchanged between two identical molecules of double-stranded or single-stranded nucleic acids such as DNA or RNA, whereas in site-specific recombination, DNA strand exchange takes place between DNA segments that possess at least a certain degree of sequence homology but no extensive homology.
Recombination is the process by which pieces of DNA are broken and recombined to produce new combinations of alleles. This process creates genetic diversity among different organisms. It is also called genetic reshuffling. It is defined as the process in which the exchange of genetic material between different organisms occurs to produce offspring with new combinations of alleles that differ from those found in either parent. Homologous recombination and site-specific recombination are two types of recombination mechanisms.
CONTENTS
1. Overview and Key Difference
2. What is Homologous Recombination
3. What is Site-Specific Recombination
4. Similarities – Homologous and Site-Specific Recombination
5. Homologous Recombination vs Site-Specific Recombination in Tabular Form
6. Comparison Summary
What is Homologous Recombination?
Homologous recombination is a type of genetic recombination in which genetic material is exchanged between two similar (identical) molecules of double-stranded or single-stranded nucleic acids (DNA or RNA). It is widely used by cells to repair harmful breaks that occur in both DNA strands, known as double-strand breaks (DSB). This process is called homologous recombinational repair (HRR). Also, homologous recombination in eukaryotes produces new combinations of DNA sequences during meiosis. Meiosis is the process by which eukaryotes make gametes such as sperms and egg cells.
Figure 01: Homologous Recombination
Homologous Recombination Mechanism
During meiosis, the paired chromosomes from the male and the female parent align so that similar DNA sequences from paired chromosomes have an opportunity to cross over one another. This crossing over results in the shuffling of genetic materials. Homologous recombination takes place with the help of proteins such as PRDM9, SPO11, DMC1, ZCWPW1, RPA, Dna2, BLM, CtIP, BRCA1, BRCA2, etc. These new combinations of DNA or alleles produce genetic variation in offspring. It enables the population to adapt during the course of evolution.
Homologous recombination is also used by bacteria and viruses. This is called “horizontal gene transfer”, a process that exchanges genetic material between different strains and species of bacteria and viruses.
What is Site-Specific Recombination?
Site-specific recombination is a type of genetic recombination in which DNA strand exchange takes place between DNA segments possessing at least a certain degree of sequence homology but no extensive homology. It occurs in bacterial genome replication, differentiation pathogenesis, and movement of mobile genetic element.
Site-specific Recombination Mechanism
Enzymes that are known as site-specific recombinases (SSRs) are involved in this process. They recognize and bind to short and specific DNA sequences. Then they cleave the DNA backbone and exchange the two DNA helices involved. Ultimately, these enzymes re-join the DNA strands.
Figure 02: Site-Specific Recombination
In most cases, the presence of a recombinase enzyme and recombination sites are sufficient for this process. But in some cases, a number of accessory proteins or accessory sites are required. Site-specific recombination systems are highly specific, fast, and efficient. Therefore, they are potential tools for genetic engineering.
What are the Similarities Between Homologous Recombination and Site-Specific Recombination?
- They are types of recombination mechanisms.
- They enhance genetic variation among different organisms.
- Both processes occur between DNA.
- They use specific proteins for recombination mechanism.
- Both take place in prokaryotes as well as in eukaryotes.
What is the Difference Between Homologous Recombination and Site-Specific Recombination?
Homologous recombination is a type of genetic recombination in which genetic material is exchanged between two identical molecules of double-stranded or single-stranded nucleic acids such as DNA or RNA. On the other hand, Site-specific recombination is a type of genetic recombination in which DNA strand exchange takes place between DNA segments that possess at least a certain degree of sequence homology but no extensive homology. So, this is the key difference between homologous recombination and site-specific recombination. Moreover, homologous recombination occurs between long DNA strands. In contrast, site-specific recombination occurs between short DNA sequences. Thus, this is another significant difference between homologous recombination and site-specific recombination.
Below is a list of differences between homologous recombination and site-specific recombination in tabular form.
Comparison Summary – Homologous vs Site-Specific Recombination
Genetic recombination involves the exchange of genetic material either between multiple chromosomes or between different regions of the same chromosome. Homologous recombination and site-specific recombination are two types of recombination mechanisms. Homologous recombination occurs between DNA with extensive sequence homology. Site-specific recombination occurs between DNA with no extensive homology. Thus, this summarizes the difference between homologous recombination and site-specific recombination.
Reference:
1. Heyer, Wolf-Dietrich, et al. “Regulation of Homologous Recombination in Eukaryotes.” Annual Review of Genetics, U.S. National Library of Medicine, 2010, Available here.
2. “Site-Specific Recombination.” Site-Specific Recombination – an Overview | ScienceDirect Topics, Available here.
Image Courtesy:
1. “HR in meiosis” By Emw – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “SUrot” By Juergen Bode – Own work (CC BY-SA 3.0) via Commons Wikimedia