horizontal gene transfer

Examples of horizontal gene transfer in the following topics:

• Horizontal Gene Transfer

  • Horizontal gene transfer (HGT) is the passing of genetic material between species by mechanisms other than from parent to offspring.
  • Horizontal gene transfer (HGT) is the introduction of genetic material from one species to another species by mechanisms other than the vertical transmission from parent(s) to offspring.
  • Horizontal gene transfer is the introduction of genetic material from one species to another species by mechanisms other than the vertical transmission from parent(s) to offspring.
  • Examples of mechanisms of horizontal gene transfer are listed for both prokaryotic and eukaryotic organisms.
  • Explain how horizontal gene transfer can make resolution of phylogenies difficult

• Genomic Similiarities between Distant Species

  • In addition, the mechanisms by which genomic similarities between distant species occur can include horizontal gene transfer.
  • Horizontal gene transfer (HGT), also known as lateral gene transfer, is the transfer of genes between unrelated species.
  • These gene transfers between species are the major mechanism whereby bacteria acquire resistance to antibiotics.
  • Although it is easy to see how prokaryotes exchange genetic material by HGT, it was initially thought that this process was absent in eukaryotes, followed by the idea that the gene transfers between multicellular eukaryotes should be more difficult.
  • According to DNA analysis, this ability is due to the transfer of fungal genes into the insect by HGT, presumably as the insect consumed fungi for food .

• Web, Network, and Ring of Life Models

  • The recognition of the importance of Horizontal gene transfer (HGT), especially in the evolution of prokaryotes, has caused some to propose abandoning the classic "tree of life" model.
  • The hypothesis is that eukaryotes evolved not from a single prokaryotic ancestor, but from a pool of many species that were sharing genes by HGT mechanisms.
  • Some individual prokaryotes were responsible for transferring the bacteria that caused mitochondrial development in the new eukaryotes, whereas other species transferred the bacteria that gave rise to chloroplasts.
  • Using the conditioned reconstruction algorithm, it proposes a ring-like model in which species of all three domains (Archaea, Bacteria, and Eukarya) evolved from a single pool of gene-swapping prokaryotes.
  • Ford Doolittle, the "tree of life" arose from a community of ancestral cells, has multiple trunks, and has connections between branches where horizontal gene transfer has occurred.

• Limitations to the Classic Model of Phylogenetic Trees

  • The concept of genes being transferred between unrelated species was not considered as a possibility until relatively recently.
  • Horizontal gene transfer (HGT), also known as lateral gene transfer, is the transfer of genes between unrelated species.
  • Genes have been shown to be passed between species which are only distantly related using standard phylogeny, thus adding a layer of complexity to the understanding of phylogenetic relationships.
  • Finally, as an example of the ultimate gene transfer, theories of genome fusion between symbiotic or endosymbiotic organisms have been proposed to explain an event of great importance: the evolution of the first eukaryotic cell, without which humans could not have come into existence.

• Modern Applications of DNA

  • It is now also possible to determine predispositions to some diseases by looking at genes.
  • CRISPR (Clustered, Regularly-Interspaced Short Palindromic Repeats) allows scientists to edit genomes, far better than older techniques for gene splicing and editing.
  • The CRISPR technique has enormous potential application, including altering the germline of humans, animals and other organisms, and modifying the genes of food crops.
  • Genetic modification involves the mutation, insertion, or deletion of genes.
  • Inserted genes usually come from a different species in a form of horizontal gene-transfer.

• Endosymbiotic Theory and the Evolution of Eukaryotes

  • Scientists believe the ultimate event in HGT (horizontal gene transfer) occurs through genome fusion between different species when two symbiotic organisms become endosymbiotic.
  • This occurs when one species is taken inside the cytoplasm of another species, which ultimately results in a genome consisting of genes from both the endosymbiont and the host.
  • Using DNA analysis and a new mathematical algorithm called conditioned reconstruction (CR), it has been proposed that eukaryotic cells developed from an endosymbiotic gene fusion between two species: one an Archaea and the other a Bacteria.
  • As mentioned, some eukaryotic genes resemble those of Archaea, whereas others resemble those from Bacteria.
  • Most interestingly, the eukaryote-first hypothesis proposes prokaryotes actually evolved from eukaryotes by losing genes and complexity .

• Genetic Engineering

  • 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.
  • Although classical methods of studying the function of genes began with a given phenotype and determined the genetic basis of that phenotype, modern techniques allow researchers to start at the DNA sequence level and ask: "What does this gene or DNA element do?
  • Similarly, mutating or deleting genes provides researchers with clues about gene function.
  • The methods used to disable gene function are collectively called gene targeting.
  • Gene targeting is the use of recombinant DNA vectors to alter the expression of a particular gene, either by introducing mutations in a gene, or by eliminating the expression of a certain gene by deleting a part or all of the gene sequence from the genome of an organism.

• The Evolution of Mitochondria

  • Mitochondria have their own circular DNA chromosome that is stabilized by attachments to the inner membrane and carries genes similar to genes expressed by alpha-proteobacteria.
  • Mitochondria also have special ribosomes and transfer RNAs that resemble these components in prokaryotes.
  • This has been interpreted as evidence that genes have been transferred from the endosymbiont chromosome to the host genome.
  • Despite the transfer of genes between mitochondria and the nucleus, mitochondria retain much of their own independent genetic material.
  • Another possible explanation is that there are differences in codon usage between the nucleus and mitochondria, making it difficult to be able to fully transfer the genes.

• Genetically Modified Organisms (GMOs)

  • Gene transfer occurs naturally between species in microbial populations.
  • In plants, tumors caused by the bacterium Agrobacterium tumefaciens occur by transfer of DNA from the bacterium to the plant.
  • Researchers used the natural transfer of DNA from Agrobacterium to a plant host to introduce DNA fragments of their choice into plant hosts.
  • Researchers manipulate the Ti plasmids to remove the tumor-causing genes and insert the desired DNA fragment for transfer into the plant genome.
  • The crystal toxin genes have been cloned from Bt and introduced into plants.

• Chromosomal Structural Rearrangements

  • 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.
  • Unless they disrupt a gene sequence, inversions only change the orientation of genes and are likely to have milder effects than aneuploid errors.
  • However, altered gene orientation can result in functional changes because regulators of gene expression could be moved out of position with respect to their targets, causing aberrant levels of gene products.
  • This suggests that one of the inversion breakpoints occurred between these two genes.
  • A reciprocal translocation occurs when a segment of DNA is transferred from one chromosome to another, nonhomologous chromosome.