recombinant DNA

Examples of recombinant DNA in the following topics:

• 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).

• Gene rearrangement within genomes

  • 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.
  • 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.
  • Recombination can occur between DNA sequences that contain no sequence homology.

• Molecular and Cellular Cloning

  • Addition of an enzyme called DNA ligase permanently joins the DNA fragments via phosphodiester bonds.
  • 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.

• Genetically Modified Organisms (GMOs)

  • Transgenic modification, adding recombinant DNA to a species, has led to the expression of desirable genes in plants and animals.
  • 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.
  • Researchers used the natural transfer of DNA from Agrobacterium to a plant host to introduce DNA fragments of their choice into plant hosts.

• 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.
  • The DNA transferred can be in the form of a plasmid or as a hybrid, containing both plasmid and chromosomal DNA.
  • The DNA may remain separate as plasmid DNA or be incorporated into the host genome.
  • In (b) transduction, a bacteriophage injects DNA into the cell that contains a small fragment of DNA from a different prokaryote.

• Genetic Maps

  • The term linkage was used before the discovery of DNA.
  • 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.
  • 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 .
  • Non-coding DNA has no known biological function; however, research shows that much of this DNA is actually transcribed.
  • Some parts of the genome are recombination hotspots, whereas others do not show a propensity for recombination.

• Variations in Size and Number of Genes

  • Also, when the offspring's chromosomes are copied after fertilization, genes can be exchanged in a process called sexual recombination.
  • Harmless mutations and sexual recombination may allow the evolution of new characteristics.
  • Genome size is usually measured in base pairs (or bases in single-stranded DNA or RNA).
  • Different species can have different numbers of genes within the entire DNA or genome of the organism.
  • Genome size can increase by duplication, insertion, or polyploidization and the process of recombination can lead to both DNA loss or gain.

• DNA Repair

  • DNA replication is a highly accurate process, but mistakes can occasionally occur as when a DNA polymerase inserts a wrong base.
  • The segment of DNA is removed and replaced with the correctly-paired nucleotides by the action of DNA pol.
  • Errors during DNA replication are not the only reason why mutations arise in DNA.
  • A special enzyme, DNA ligase (shown here in color), encircles the double helix to repair a broken strand of DNA.
  • DNA ligases catalyse the crucial step of joining breaks in duplex DNA during DNA repair, replication and recombination, and require either Adenosine triphosphate (ATP) or Nicotinamide adenine dinucleotide (NAD+) as a cofactor.

• Gene Duplications and Divergence

  • Gene duplication is the process by which a region of DNA coding for a gene is copied.
  • 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.
  • 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 .
  • During replication, DNA polymerase begins to copy the DNA, and at some point during the replication process, the polymerase dissociates from the DNA and replication stalls.

• Genetic Linkage and Distances

  • Linked genes can become unlinked during recombination; the probability of genes separating depends on their distance from each other.
  • When synapsed, homologous chromosomes undergo reciprocal physical exchanges of DNA at their arms in a process called homologous recombination, or more simply, "crossing over."
  • 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.
  • This genetic map orders Drosophila genes on the basis of recombination frequency.