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Vertical gene transfer is common in all organisms, while horizontal gene transfer is not. Single-celled organisms, especially bacteria, acquire genetic material through horizontal gene transfer, which allows them to maintain diversity. Bacteria can exchange genetic material through transformation, transduction, and bacterial conjugation. Some eukaryotes, including fungi, insects, and plants, also engage in horizontal gene transfer. Viruses can also transmit genetic information through horizontal gene transfer. Mimivirus, Mamavirus, and Sputnik are known hosts of horizontal gene transfer.
Virtually all organisms can spread genetic material via vertical gene transfer in which genetic information is passed on from parents to offspring. In contrast, the process of horizontal gene transfer – or lateral gene transfer – is not common to all species. In this type of gene transfer, genetic material is passed between organisms that are not parents and offspring. Instead, the two organisms are generally unrelated and are often of different species.
Most eukaryotic organisms acquire genetic material primarily through vertical gene transfer, during which recombination of DNA occurs. Conversely, horizontal gene transfer is thought to be the most common way that single-celled organisms, especially bacteria, acquire new genetic material. This is important because bacteria reproduce without sexual recombination; thus horizontal transfer allows bacterial species to maintain diversity.
Horizontal gene transfer in bacteria is a common phenomenon. There are three ways bacteria can exchange genetic material horizontally. All three of these occur naturally and can even be done in the laboratory to genetically engineer bacteria with novel properties, such as the ability to synthesize non-native proteins.
Transformation is a process in which bacteria ingest naked DNA or RNA molecules and express them within the cell. In transduction, genetic material is transferred by bacteriophages, which are viruses that infect bacteria. Finally there is bacterial conjugation, in which genetic material, often plasmids, is transferred via cell-to-cell contact. Conjugation is mediated by transposons and plasmids, two distinct and independent types of genetic material from the bacterial genome.
There is some evidence that viruses can also transmit genetic information via horizontal gene transfer. One of the strongest indicators involves viruses called Mimivirus, Mamavirus and Sputnik. Both Mimivirus and Mamavirus are known hosts of Sputnik, and a small number of genes are common to all three species. Sputnik is thought to have transferred genes between its two host viruses at some point during the evolutionary history of these three organisms.
Some eukaryotes, including species of fungi, insects, and plants, also engage in horizontal gene transfer. One of the best-known examples is horizontal gene transfer between bacteria and Saccharomyces cerevisiae, a species of yeast. Another example of gene transfer between eukaryotes involves the azuki bean beetle and a bacterium called Wolbachia. In the plant world, parasites of a plant family called Rafflesiaceae have transferred genetic information to their hosts, and a species of algae has transferred genetic material to a species of sea snail that preys on algae.
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