Table 1.
Mechanisms of lateral genetic transfer and/or exchange.
| Organisms involved (mechanism) | MGEa and/or agent involved | Frequency of occurrence | Magnitude of genetic transfer/exchange relative to host’s genome | Accumulation and integration of genetic material into host’s genome over time | Detectability of source of origin (donor) after eons |
|---|---|---|---|---|---|
| Virus-to-, or unicellular-to-unicellular | |||||
| Virus-mediated (transduction) | |||||
| Virus-to-prokaryote | Bacteriophagesb | High | Low to medium | Probably high | Probably low |
| Virus-to-eukaryote | Transposons | High | Low | Moderate | Probably low |
| Prokaryote-to-prokaryote | |||||
| (transformation) | Gene fragments | High | Low to medium | Moderate | Low to moderate |
| (conjugation) | Plasmids | High | Low to high | Moderate to high | Moderate |
| Prokaryote-to-eukaryote | |||||
| (symbiogenesis) | Cells | Low to high | Low to medium | Low to moderate | Low |
| (phagotrophism) | Cells | Probably high | Low to medium | Low to moderate | Low |
| Eukaryote-to-eukaryote | |||||
| (phagotrophism) | Cells | Low to high | Low to medium | Low to moderate | Low |
| (nuclear exchange) | Micro-nuclei | Probably high | Medium | High | Moderate to high |
| Virus-to-, unicellular-to-, or multicellular-to-multicellular | |||||
| Virus-to-plants/animals/fungi (transposition) | Transposonsc | High | Low | Low to moderate | Low |
| Bacteria-to-plants/animals/fungi (transfer)d | Plasmids or gene fragments | Low to high | Low to medium | Low to moderate | Low to moderate |
| Plants-to-plants (hybridization) | Gametes | Low to high | High | High | Moderate to high |
| Animals-to-animals (hybridization) | Gametes | Low to medium | High | High | High |
| Multicellular-to-virus, or unicellular | |||||
| Plants/animals/fungi-to-virus (transfer) | Gene fragments | High | High | High | Low |
| Plants/animals/fungi-to-prokaryote (transformation)e | Gene fragments | High | High | Moderate | Low |
| Plants/animals/fungi-to-eukaryote (transfer)e | Gene fragments | Low to high | Low to medium | Low to moderate | Low |
Mobile Genetic Elements are fragments of genetic material that “move” within and among genomes.
Bacteriophages can be considered both organism-participants in HGT and “agent” mediators of lateral genetic transfer.
Transposons in multicellular organisms include “transposable elements” or “jumping genes”.
Gene transfer from bacteria to plants (e.g. conjugative plasmids for nitrogen fixation) and animals (e.g. nematode parasitic genes obtained from prokaryotes; rotifers’ acquisition of pro and eukaryotic genes) has been documented (Keeling and Palmer 2008; Mitreva, Smant, and Helder 2009).
Metabolic and structural gene or gene-fragment transfer from multi to unicellular organisms is increasingly being reported (Keeling and Palmer 2008).