Exchange and absorption of genetic material independent of reproduction: independent of the vertical transfer of passing genes from parental to the following generations via sexual or asexual reproduction.
Horizontal gene transfer (HGT) enables the sharing of genetic material evolved in one group of organisms with other groups. HGT appears more frequent between closely related organisms like strains of the same or closely related bacterial species. Genes are also transferred between more distant species, but might have a lower success rate to become permanently integrated.
Horizontal gene transfer has a strong impact on the evolution of bacteria. Beside reproduction, new genes are acquired by:
transformation: absorbing genetic material from environment
transduction: infection by lysogenic phages leads to genetic material built in the bacterial genome
conjugation: genetic material exchanged between bacteria of the same species
Horizontally transferred genes can be identified by comparing the evolutionary history of single genes with the history of the species.
Phylogenetic conflict: By comparing the phylogenetic tree of a gene and the tree of a species, differences in branching patterns can be used to identify the HGT event and possible transfer route.
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