homologous recombination

Examples of homologous recombination in the following topics:

• Generalized Recombination and RecA

  • In homologous recombination, a type of genetic recombination, nucleotide sequences are exchanged between two similar molecules of DNA.
  • Homologous recombination is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA.
  • Homologous recombination is conserved across all three domains of life as well as viruses.
  • Homologous recombination is a major DNA repair process in bacteria.
  • Homologous recombination has been most studied and is best understood for Escherichia coli.

• Genetic Linkage and Distances

  • As chromosomes condensed and paired with their homologs, they appeared to interact at distinct points.
  • It is now known that the pairing and interaction between homologous chromosomes, known as synapsis, does more than simply organize the homologs for migration to separate daughter cells.
  • When synapsed, homologous chromosomes undergo reciprocal physical exchanges of DNA at their arms in a process called homologous recombination, or more simply, "crossing over."
  • He also assumed that the incidence of recombination between two homologous chromosomes could occur with equal likelihood anywhere along the length of the chromosome.
  • A recombination frequency of 0.5 indicates that 50 percent of offspring are recombinants and the other 50 percent are parental types .

• Gene rearrangement within genomes

  • During meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes.
  • Crossing-over (homologous recombination) is one such mechanism by which DNA variations can occur, and genes can be rearranged.
  • In meiosis and mitosis, recombination occurs between similar molecules (homologs) of DNA.
  • In both meiotic and mitotic cells, recombination between homologous chromosomes is a common mechanism used in DNA repair.
  • Recombination can occur between DNA sequences that contain no sequence homology.

• Mu: A Double-Stranded Transposable DNA Bacteriophage

  • Once the viral DNA is inserted into the bacteria, the Mu's transposase protein/enzyme in the cell recognizes the recombination sites at the ends of the viral DNA (gix-L and gix-R sites) and binds to them, allowing the process of replicating the viral DNA or embedding it into the host genome.
  • Its transposition mechanism is somewhat similar to a homologous recombination.

• Genetic Linkage and Violation of the Law of Independent Assortment

  • Genes that are located on separate non-homologous chromosomes will always sort independently .
  • Homologous chromosomes possess the same genes in the same linear order.
  • Like genes on the homologs align with each other.
  • The process of crossover, or recombination, occurs when two homologous chromosomes align during meiosis and exchange a segment of genetic material.
  • The result is two recombinant and two non-recombinant chromosomes.

• Genetically Engineered Vaccines

  • Gene targeting is a different technique that uses homologous recombination to change an endogenous gene, and can be used to delete a gene, remove exons, add a gene, or introduce point mutations.
  • Despite the early success demonstrated with the hepatitis B vaccine, no other recombinant engineered vaccine has been approved for use in humans.
  • Although recombinant subunit vaccines hold great promise, they do present some potential limitations.
  • Recombinant subunit vaccines may also suffer from being too well-defined, because they are composed of a single antigen.
  • This problem can be minimized, where necessary, by creating recombinant vaccines that are composed of multiple antigens from the same pathogen.

• Genetic Maps

  • The exchange of DNA between homologous pairs of chromosomes is called genetic recombination, which occurs by the crossing over of DNA between homologous strands of DNA, such as nonsister chromatids.
  • Linkage analysis involves studying the recombination frequency between any two genes.
  • The greater the distance between two genes, the higher the chance that a recombination event will occur between them, and the higher the recombination frequency between them .
  • Because genetic maps rely completely on the natural process of recombination, mapping is affected by natural increases or decreases in the level of recombination in any given area of the genome.
  • Some parts of the genome are recombination hotspots, whereas others do not show a propensity for recombination.

• Meiosis II

  • The mechanics of meiosis II is similar to mitosis, except that each dividing cell has only one set of homologous chromosomes.
  • The cells produced are genetically unique because of the random assortment of paternal and maternal homologs and because of the recombining of maternal and paternal segments of chromosomes (with their sets of genes) that occurs during crossover .
  • In prometaphase I, microtubules attach to the fused kinetochores of homologous chromosomes, and the homologous chromosomes are arranged at the midpoint of the cell in metaphase I.
  • In anaphase I, the homologous chromosomes are separated.

• Chromosomal Structural Rearrangements

  • Both are identified during meiosis by the adaptive pairing of rearranged chromosomes with their former homologs to maintain appropriate gene alignment.
  • If the genes carried on two homologs are not oriented correctly, a recombination event could result in the loss of genes from one chromosome and the gain of genes on the other.
  • When one homologous chromosome undergoes an inversion, but the other does not, the individual is described as an inversion heterozygote .
  • To maintain point-for-point synapsis during meiosis, one homolog must form a loop, and the other homolog must mold around it.
  • This inversion pairing is essential to maintaining gene alignment during meiosis and to allow for recombination.

• Isotype Class Switching

  • Class switching occurs by a mechanism called class switch recombination (CSR) binding .
  • The free ends of the DNA are rejoined by a process called non-homologous end joining (NHEJ) to link the variable domain exon to the desired downstream constant domain exon of the antibody-heavy chain.
  • In the absence of non-homologous end joining, free ends of DNA may be rejoined by an alternative pathway biased toward microhomology joins.
  • Mechanism of class switch recombination that allows isotype switching in activated B cells.
  • Describe the process of class switch recombination that results in changes in the antibody-heavy chain