What is the Difference Between Recombination and Reassortment

The main difference between recombination and reassortment is that recombination occurs when at least two viral genomes co-infect the same host cell by exchanging genetic segments, whereas reassortment is a particular type of recombination that occurs in viruses with segmented genomes by interchanging complete genome segments.  

Recombination and reassortment are two types of exchanges of genetic segments of the genomes of viruses. Both have major impacts on their evolution.

Key Areas Covered

1. What is Recombination
     – Definition, Features, Importance
2. What is Reassortment
     – Definition, Features, Importance
3. Similarities Between Recombination and Reassortment
     – Outline of Common Features
4. Difference Between Recombination and Reassortment
     – Comparison of Key Differences

Key Terms

Recombination, Reassortment

What is Recombination

Recombination is the exchange of genetic material between organisms during the production of offspring. Therefore, it is responsible for the combination of traits different from parent traits. Generally, recombination occurs during meiosis in eukaryotes. Naturally, there are two types of recombination; interchromosomal recombination and intrachromosomal recombination. Further, interchromosomal recombination occurs through the independent assortment of alleles in homologous chromosomes. In comparison, intrachromosomal recombination occurs through crossing over.

Figure 1: Recombination

Furthermore, recombination occurs in two ways: by copying genetic material from one chromosome to another or by physically rejoining DNA strands. It is a natural process regulated by enzymes such as recombinases. RecA serves as the chief recombinase that occurs in E. coli. In general, it is responsible for the repair of double-strand breaks. Apart from that, eukaryotes and yeast require two recombinases for the repair of double-strand breaks. RAD51 is responsible for meiotic and mitotic recombination, while DMC1 is a DNA repair protein. Besides, recombination maintains genetic diversity as well as genetic integrity.  

What is Reassortment

Reassortment is the exchange of genetic material as segments, forming new combinations in individuals. It is a type of recombination. In general, it occurs in influenza viruses, and the genome of these viruses contains eight RNA segments. Usually, these segments are distinct and act as mini-chromosomes. The exchange of mini-chromosomes requires the presence of one segment from each type. When the two different strains of the influenza virus co-infect the same host, the newly-assembled viruses contain segments whose origins are mixed. Therefore, some segments of a particular assembled virus come from one strain while the other segments come from another strain.

Figure 2: Reassortment

Moreover, recombination occurs when the two viruses co-infect the same host. During co-infection, the two viruses exchange genetic segments. More importantly, genetic recombination in RNA viruses leads to both the diversity of viruses as well as immune evasion. In addition, recombination determines the architecture of the genome while helping in the evolution of single-stranded RNA viruses such as poliovirus.     

Similarities Between Recombination and Reassortment

• Recombination and reassortment are two types of exchanging of genome segments.
• Both occur in DNA viruses and are infrequent in RNA viruses.
• Both are non-reciprocal, and therefore, the recipient genome portion does not act as the donor to replace the portion in the original source.
• They are important for genetic diversity and the integrity of the genome.

Difference Between Recombination and Reassortment

Definition

Recombination refers to the rearrangement of genetic material by crossing over in chromosomes or by artificially joining the segments of chromosomes of different organisms, while reassortment refers to the mixing of the genetic material of a species into new combinations in different individuals.  

Occurrence

Recombination occurs during meiosis and mitosis, whereas reassortment occurs when at least two viral genomes co-infect the same host cell by exchanging genetic segments.

Processes

While recombination occurs through chromosomal crossover and reassortment of chromosomes, reassortment occurs in viruses with segmented genomes by interchanging complete genome segments.  

Significance

Recombination is the rearrangement of genetic material, while reassortment is a particular type of recombination.

Conclusion                                                      

In brief, recombination and reassortment are two types of genetic rearrangements that occur in genomes. Generally, recombination is the rearrangement of genetic material by crossing over in chromosomes. It helps in the exchange of genetic segments of chromosomes of different organisms. Generally, it occurs during the coinfection of the same host by two viruses. In comparison, reassortment is a type of recombination that occurs in viruses with segmented genomes. In addition, it involves the interchanging of complete genome segments. Therefore, the main difference between recombination and reassortment is the form of exchange of genome segments.        

References:                

1. Pérez-Losada M, Arenas M, Galán JC, Palero F, González-Candelas F. Recombination in viruses: mechanisms, methods of study, and evolutionary consequences. Infect Genet Evol. 2015 Mar;30:296-307. doi: 10.1016/j.meegid.2014.12.022. Epub 2014 Dec 23. PMID: 25541518; PMCID: PMC7106159.

Image Courtesy:

1. “Homologous Recombination” By Harris Bernstein, Carol Bernstein and Richard E. Michod – Own work (CC BY 3.0) via Commons Wikimedia
2. “Reassortment” By Mouagip – Own Work (Public Domain) via Commons Wikimedia