recombination

Examples of recombination in the following topics:

• Gene rearrangement within genomes

  • In meiosis and mitosis, recombination occurs between similar molecules (homologs) of DNA.
  • Genetic recombination and recombinational DNA repair also occurs in bacteria and archaea.
  • Recombination can be artificially induced in laboratory (in vitro) settings, producing recombinant DNA for purposes including vaccine development.
  • V(D)J recombination in organisms with an adaptive immune system is a type of site-specific genetic recombination that helps immune cells rapidly diversify to recognize and adapt to new pathogen.
  • Recombination can occur between DNA sequences that contain no sequence homology.

• Genetic Linkage and Violation of the Law of Independent Assortment

  • Genes that are on the same chromosome, or "linked", do not assort independently, but can be separated by recombination.
  • To understand this, let's consider the biological basis of gene linkage and recombination.
  • This process is called recombination, or crossover, and it is a common genetic process.
  • Because the genes are aligned during recombination, the gene order is not altered.
  • The result is two recombinant and two non-recombinant chromosomes.

• Genetic Linkage and Distances

  • Linked genes can become unlinked during recombination; the probability of genes separating depends on their distance from each other.
  • A recombination frequency of 0.5 indicates that 50 percent of offspring are recombinants and the other 50 percent are parental types .
  • The recombination frequency will be the same as if the genes were on separate chromosomes.
  • (d) The actual recombination frequency of fruit fly wing length and body color that Thomas Morgan observed in 1912 was 17 percent.
  • This genetic map orders Drosophila genes on the basis of recombination frequency.

• Genetic Maps

  • 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.
  • Recombination between genes A and B is more frequent than recombination between genes B and C because genes A and B are farther apart; a crossover is, therefore, more likely to occur between them.

• Genetic Engineering

  • In genetic engineering, an organism's genotype is altered using recombinant DNA, created by molecular cloning, to modify an organism's DNA.
  • Genetic engineering is the alteration of an organism's genotype using recombinant DNA technology to modify an organism's DNA to achieve desirable traits.
  • Recombinant DNA technology, or DNA cloning, is the process of transferring a DNA fragment of interest from one organism to a self-replicating genetic element, such as a bacteria plasmid, which is called a vector.
  • The addition of foreign DNA in the form of recombinant DNA vectors generated by molecular cloning is the most common method of genetic engineering.
  • The organism that receives the recombinant DNA is called a genetically-modified organism (GMO).

• Molecular and Cellular Cloning

  • Plasmids with foreign DNA inserted into them are called recombinant DNA molecules because they are created artificially and do not occur in nature.
  • Proteins that are expressed from recombinant DNA molecules are called recombinant proteins.
  • Not all recombinant plasmids are capable of expressing genes.
  • The recombinant DNA may need to be moved into a different vector (or host) that is better designed for gene expression.
  • Plasmids may also be engineered to express proteins only when stimulated by certain environmental factors so that scientists can control the expression of the recombinant proteins.

• Prokaryotic Reproduction

  • Binary fission does not provide an opportunity for genetic recombination or genetic diversity, but prokaryotes can share genes by three other mechanisms .
  • Transduction results in a recombinant organism.
  • This short generation time, coupled with mechanisms of genetic recombination and high rates of mutation, result in the rapid evolution of prokaryotes, allowing them to respond to environmental changes (such as the introduction of an antibiotic) very rapidly.

• Genetically Modified Organisms (GMOs)

  • Transgenic modification, adding recombinant DNA to a species, has led to the expression of desirable genes in plants and animals.
  • Although several recombinant proteins used in medicine are successfully produced in bacteria, some proteins require a eukaryotic animal host for proper processing.
  • Animals that have been modified to express recombinant DNA are called transgenic animals.
  • Mice have been used extensively for expressing and studying the effects of recombinant genes and mutations.
  • Plants that have received recombinant DNA from other species are called transgenic plants.

• Gene Duplications and Divergence

  • Gene duplication can occur as the result of an error in recombination or through a retrotransposition event.
  • The product of this recombination is a duplication at the site of the exchange and a reciprocal deletion.
  • Ectopic recombination is typically mediated by sequence similarity at the duplicate breakpoints, which form direct repeats.
  • Repetitive genetic elements, such as transposable elements, offer one source of repetitive DNA that can facilitate recombination, and they are often found at duplication breakpoints in plants and mammals .
  • Ectopic recombination is typically mediated by sequence similarity at the duplicate breakpoints, which form direct repeats.

• Deuteromycota: The Imperfect Fungi

  • Some hyphae may recombine and form heterokaryotic hyphae.
  • Genetic recombination is known to take place between the different nuclei.