![]() The mechanism of HGT has been shown to be quite common in the prokaryotic domains of Bacteria and Archaea, significantly changing the way their evolution is viewed. Summary of Mechanisms of Prokaryotic and Eukaryotic HGT These transfers may occur between any two species that share an intimate relationship ( ). Many scientists believe that HGT and mutation appear to be (especially in prokaryotes) a significant source of genetic variation, which is the raw material for the process of natural selection. As the phenomenon is investigated more thoroughly, it may be revealed to be more common. Some researchers believe such estimates are premature: the actual importance of HGT to evolutionary processes must be viewed as a work in progress. It is thought that HGT is more prevalent in prokaryotes, but that only about 2% of the prokaryotic genome may be transferred by this process. These transfers allow even distantly related species to share genes, influencing their phenotypes. 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. 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. Although at present HGT is not viewed as important to eukaryotic evolution, HGT does occur in this domain as well. The various ways that HGT occurs in prokaryotes is important to understanding phylogenies. 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. HGT has been shown to be an ever-present phenomenon, with many evolutionists postulating a major role for this process in evolution, thus complicating the simple tree model. Horizontal gene transfer (HGT), also known as lateral gene transfer, is the transfer of genes between unrelated species. The concept of genes being transferred between unrelated species was not considered as a possibility until relatively recently. This view is somewhat complicated in eukaryotes that reproduce sexually, but the laws of Mendelian genetics explain the variation in offspring, again, to be a result of a mutation within the species. That is, they produce offspring themselves with only random mutations causing the descent into the variety of modern-day and extinct species known to science. However, evidence from modern DNA sequence analysis and newly developed computer algorithms has caused skepticism about the validity of the standard tree model in the scientific community.Ĭlassical thinking about prokaryotic evolution, included in the classic tree model, is that species evolve clonally. The concept of a phylogenetic tree with a single trunk representing a common ancestor, with the branches representing the divergence of species from this ancestor, fits well with the structure of many common trees, such as the oak ( b). Phylogenetic trees originated with Charles Darwin, who sketched the first phylogenetic tree in 1837 ( a), which served as a pattern for subsequent studies for more than a century. Many phylogenetic trees have been shown as models of the evolutionary relationship among species. New models of these relationships have been proposed for consideration by the scientific community. Over the last several decades, new research has challenged scientists’ ideas about how organisms are related. It is one of the most dynamic fields of study in all of biology. The concepts of phylogenetic modeling are constantly changing. ![]() Identify the web and ring models of phylogenetic relationships and describe how they differ from the original phylogenetic tree concept.Illustrate how prokaryotes and eukaryotes transfer genes horizontally.By the end of this section, you will be able to:
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