Homologous Recombination

“Homologous recombination is the exchange of genetic information between two similar or identical strands of a double-stranded DNA molecule.”

It is also known as general recombination. It occurs in eukaryotes, bacteria and viruses naturally. It is very useful in genetic engineering techniques.

Homologous Recombination in Eukaryotes

DNA Repair

Homologous recombination plays an important role in repairing damaged DNA. DNA strands that are damaged by ionizing radiation or chemicals undergo recombination during mitosis to overcome the injury. If left unrepaired, these broken DNA can go on to amplify and cause mutations in the genome.

Genetic Diversity

The sex cells undergo meiosis to produce specialised cells called ovum and sperm. During the process of meiosis, chromosomal crossover takes place which is the exchange of genetic material between homologous chromosomes. This event of recombination brings genetic diversity every time an organism reproduces.

The phenomena of crossing over between two homologous chromosomes.

Homologous Recombination in Bacteria

Horizontal Gene Transfer

Horizontal gene transfer is the phenomenon of transferring foreign DNA into another organism without being related to it. The incoming DNA is highly similar to the receiver’s DNA, and they undergo homologous recombination to incorporate the foreign DNA.

Bacterial Transformation

Transformation is the process of the transfer of DNA from one organism to another within the same species. They undergo homologous recombination to incorporate the donor DNA by binding to several proteins, which make the cells competent to take up the DNA.

Similar to eukaryotes, homologous recombination also helps in DNA repair and brings about genetic diversity in bacteria.

Homologous Recombination in Viruses

In viruses, homologous recombination occurs both in DNA and RNA strands. It helps in viral evolution when two separate viral genomes with disadvantageous mutations undergo recombination and produce a fully functional genome.

Homologous recombination is also a primary phenomenon in the incorporation of human herpesvirus – 6 in human telomeres causing rashes, fever and diarrhea in infants and children.

Covid-19 caused by the SARS-Cov-2 virus is also a result of viral evolution by homologous recombination.

Homologous Recombination and Genetic Engineering

Homologous recombination is used in genetic engineering to knock out defected or mutated genes. The mutated genes are introduced into a cell, where it recognizes a similar sequence of the foreign gene, undergoes recombination, knocks out the defected sequence and replicates to form a functional gene. It can also be used in gene targeting in knockout mice models, where sequences of your choice can be knocked out of the organism.

Disadvantages of Homologous Recombination

Improper recombination can bring out many abnormalities in a genome. During gamete formation, chromosomes can align incorrectly and result in too many or too few chromosomes in the sperm and ovum.

Down’s syndrome, an abnormality in chromosome 21 is a result of the failure of homologous recombination.

Cancer is also related to the dysfunction of chromosomal recombination.

Applications

  • Gene targeting, as described in knockout mice models, is a method to create recombinant DNA genetically modified organisms.
  • Protein engineering is the formation of a new protein by joining two genes that code for separate proteins. It brings about diversity in the protein sequence
  • It is also helpful in cancer therapy by helping in repairing the DNA damage.

Frequently Asked Questions

What is another name for homologous recombination?

Homologous recombination is also known as general recombination.

What is the difference between homologous and non-homologous recombination?

Homologous recombination is the exchange of genetic materials between similar and identical DNA strands, whereas non-homologous recombination is the addition of new material to the genetic sequence.

What phase does homologous recombination occur in meiosis?

Homologous recombination occurs during Prophase I of the cell cycle.

Is homologous recombination the same as crossing over?

Crossing over is a phenomenon of homologous recombination that occurs during meiosis.

Does recombination occur in mitosis?

Yes, mitotic recombination occurs during the preparation of the cell cycle.

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