What is Genetic Recombination?

Recombination is crucial to this process because it allows genes to be reassorted into diverse combinations. Genetic recombination is the process of combining genetic components from two different origins into a single unit. In prokaryotes, genetic recombination takes place by the unilateral transfer of deoxyribonucleic acid. It includes transduction, transformation, and conjugation. The genetic exchange occurring between homologous deoxyribonucleic acid sequences (DNA) from two different sources is termed general recombination. For this to happen, an identical sequence of the two recombining molecules is required. The process of genetic exchange which occurs in eukaryotes during sexual reproduction such as meiosis is an example of this type of genetic recombination.

Types of Genetic Recombination

Genetic recombination is mainly classified into three types homologous, non-homologous, and site-specific recombination.

Homologous recombination

Homologous recombination is a method of genetic recombination in which the nucleotide sequences of two similar or identical deoxyribonucleic acids (DNA) molecules are replaced. It is used by cells to effectively repair double-strand breaks, which are damaging in both strands of the deoxyribonucleic acid. Horizontal gene transfer uses homologous recombination to transfer genetic material across bacteria and viruses of different strains and species. Homologous recombination is used in gene targeting—a technique for introducing genetic alteration into a target species.

Non-homologous recombination

Nonhomologous recombination is a significant route for somatic cell deoxyribonucleic acid repair of chromosomal double-strand breaks. The two types of chromosomes recognized based on the pairing pattern of chromosomes during metaphase one of meiosis one are homologous and non-homologous chromosomes. Nonhomologous chromosomes are referred to as chromosomes that are not identical or similar. Non-homologous recombination is a major pathway for the repair of chromosomal double-stranded breaks in the deoxyribonucleic acid in somatic cells. In this process, two non-identical chromosomes align side by side to facilitate the restoration of a damaged segment or segments of the deoxyribonucleic acid.

The diagrammatic representation of homologous and non-homologous recombination is shown in the figure.

Site-specific Recombination

Site-specific recombination is a type of genetic recombination in which deoxyribonucleic acid strands exchange places between regions with or without homologous sequences. By identifying and binding to short deoxyribonucleic acid sequences, site-specific recombinases (SSRs) undertake deoxyribonucleic acid segment rearrangements. The site-specific recombination is different from other general recombinations. It mainly occurs between attachment sites of bacteria and attachment sites of phages. SSRs have required only short stretches of homologous sequences. Chromosomal sequences are altered by SSRs. Lysogenic integration of the phage alpha chromosome into E.coli chromosomes is one of the examples of site-specific genome recombination. The integration of the phage chromosome into a bacterium is a circular permutation. It recognizes the order of the phage chromosome’s genes.

The diagrammatic representation of Site-specific recombination is shown in the figure.
CC BY-SA 3.0 | Image Credits: https://commons.wikimedia.org | Juergen Bode

Recombination enzymes

In genetic recombination, various enzymes participate to complete the process. The genes are coded by enzymes. The first used enzymes in genetic recombination were initially isolated from E. coli. The recA gene encodes a protein required for strand invasion, whereas the rec-B, rec-C, and rec-D genes encode three polypeptides that combine to create the RecBCD protein complex. RecBCD is a protein complex in E. coli that can unwind double-stranded deoxyribonucleic acid and break strands. Branch migration is catalyzed by two additional genes, ruvA and ruv-B. Whereas, Holiday junctions are resolved by the protein resolvase, which is produced by the ruvC gene. Several enzymes, such as ligase and deoxyribonucleic acid polymerase, are included in deoxyribonucleic acid replication. In eukaryotic cells, genome recombination has been studied in yeast cells.

Benefits and applications of genetic recombination

Genetic recombination possesses a kind of benefits such as;

  1. It generate a new combination of alleles or a variety of offspring. Negative selection can eliminate harmful alleles from a population without eliminating the entire chromosomes that carries them.
  2. Homologous recombination emphasize genomic integration and shows efficiency in genome modification.
  3. Site-specific recombination systems are dominant to genome modifiers. In vitro, site-specific recombination is used in deoxyribonucleic acid cloning.
  4. Genetic recombination is used to make transgenic cells and organisms. The deoxyribonucleic acid recombinant technology helps to make microbes, plants and animals that carry genes from the other species. One of the most prominent examples of recombination is when homologous chromosomes line up in pairs and exchange segments of deoxyribonucleic acid during meiosis.

Context and Applications

This topic is important in professional exams such as school level, undergraduate, and graduate levels, especially for

  • Bachelors of Science in Molecular Biology
  • Bachelors of Science in Biochemistry
  • Masters of Science in Molecular biology
  • Masters of Science in Biochemistry

Practice Problems

Question 1: What are bacteriocins?

  1. Proteins
  2. Plasmids
  3. Sex factor
  4. Toxins

Answer: Option A is correct.

Explanation: Bacteriocins are proteins that kill the same or closely related species of bacteria and are formed by bacteriocinogenic factors. Bacteriocins are used for food preservation, as anticancerous agents, and therapeutic purposes, such as treatment for peptic ulcers.

Question 2: Remarkable capacity of short segments of the deoxyribonucleic acid moves from one place to another is called as __________

  1. Deoxyribonucleic acid replication
  2. Transcription
  3. Deoxyribonucleic acid transposition

Answer: Option C is correct.

Explanation: A short segment of deoxyribonucleic acid with the remarkable capacity to move from one location in a chromosome to another is called deoxyribonucleic acid transposition. One or more proteins termed transposases, which are usually encoded by the mobile element itself, help the mobile element move.

Question 3: Resolvase is called as _______.

  1. Rec-A
  2. Rec-B
  3. Rec-C
  4. Rec-BCD

Answer: Option D is correct.

Explanation: Rec-BCD enzyme, which has both helicase and nuclease functions, is encoded by the rec-B, rec-C, and rec-D genes in E. coli.

Question 4: The transfer of genome from one cell to another cell by bacteriophage is called as ________.

  1. Transformation
  2. Transduction
  3. Conjugation

Answer: Option B is correct.

Explanation: In prokaryotes, genetic recombination is taken place in three types, transformation, transduction, and conjugation. In transduction, the genome is transferred from one cell to another cell by bacteriophage. The virus that infects the bacteria is called a bacteriophage.

Question 5: Which enzymes are used to cut the DNA fragment?

  1. Exonuclease
  2. Restriction endonuclease
  3. DNA ligase

Answer: Option B is correct. 

Explanation: The restriction endonuclease is enzymes that produce internal cuts, called cleavage in the deoxyribonucleic acid molecule. Restriction endonuclease is a bacterial enzyme that cuts dsDNA into fragments after recognizing a specific nucleotide sequence called a recognition or restriction site.

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