A mechanism for evolution where big chunks of DNA migrate between different species via bacteria. This results in faster and more sudden evolutionary branching than what you get with the more familiar mechanisms of sexual selection or random single-point

a massive network of recent gene exchange connecting bacteria from around the world: 10K unique genes flowing via HGT among 2235 bacterial genomes.

2008-10-05: The transfer can lead to recursive genomes

Scientists have discovered a copy of the entire genome of a bacterial parasite residing inside the genome of its host species. Lateral gene transfer may happen much more frequently between bacteria and multicellular organisms than scientists previously believed, with dramatic implications for evolution. This may allow species to acquire new genes and functions extremely quickly.

2013-11-12: The transfer can also be time-shifted

You can compare it to a bunch of bacteria which poke around a trash pile looking for fragments they can use. Occasionally they hit some ‘second-hand gold,’ which they can use right away. At other times they run the risk of cutting themselves up. There is potential risk when multi-resistant bacteria exchange small fragments of ‘dangerous’ DNA, e.g., at hospitals, in biological waste and in wastewater.

2021-06-09: It might even happen in animals, perhaps via sperm.

The barriers to horizontal transfer in eukaryotes looked insurmountable until the herring genome was published. The herring genome holds many copies of transposons, mobile chunks of DNA that can copy and paste themselves in a genome, but they are absent from other fish with 1 exception. 3 of them flank the rainbow smelt’s AFP gene, in the same order seen around the herring AFP gene. These sequences are “definitive proof” that a small chunk of a herring chromosome made its way into a smelt’s. 94% of the transfers involved ray-finned fishes; less than 3% involved birds or mammals. The explanation could hinge on herring’s famously exuberant spawning efforts. The vast majority of sperm fail to find eggs, degrade, and release their DNA. The DNA could stick to the gametes from other species spawning in the same area, and then get dragged into an egg cell during fertilization.

2021-10-21: It also happens in the human microbiome, which is less surprising since that’s just bacteria.

when humans started to colonize the island of japan 40 ka ago, they did not have the genes for digesting seaweed. Bacteria in the japanese gut borrowed the necessary genes from marine bacteria via horizontal gene transfer, and since the adaption proved evolutionarily beneficial, it was preserved. of course, anti-GMO nuts fear this horizontal gene transfer the most (if they are scientifically literate enough to understand the concept, and not just spout confused concepts like “natural” vs “artificial”). it should be quite obvious from this awesome example that mammals have had to cope with horizontal gene transfer throughout their history. GMO offers nothing new we haven’t encountered before.

2022-10-28: Transfer via viruses or parasites could explain how HGT happens between Eukaryotes.

The involvement of viruses could also help to solve another puzzle about horizontal transfers in eukaryotes. For the transfers to occur, the traveling genes need to clear an entire series of hurdles. First they must get from the donor species to the new host species. Then they must get into the nucleus and ensconce themselves in the host genome. But getting into the genome of just any cell won’t do: In multicellular creatures like frogs and herrings, a gene won’t be passed down to the animal’s offspring unless it can sneak into a germline cell — a sperm or an egg.

Is there something about the environment of Madagascar that makes it a hot spot for gene transfers? The abundance of parasites on the island might also be a contributing factor. Leeches may bring blood containing the snake’s jumping gene into the frogs, or perhaps the jumping gene is already in the leech’s own genome from previous contacts with snakes. Then maybe an unidentified virus does the rest.

2023-01-19: Tycheposons

The findings describe a new class of genetic agents involved in horizontal gene transfer, in which genetic information is passed directly between organisms — whether of the same or different species — through means other than lineal descent. The researchers have dubbed the agents that carry out this transfer “tycheposons,” which are sequences of DNA that can include several entire genes as well as surrounding sequences, and can spontaneously separate out from the surrounding DNA. Then, they can be transported to other organisms by one or another possible carrier system including tiny bubbles known as vesicles that cells can produce from their own membranes.

2023-08-04: Mavericks, or Polintons, are large DNA transposons that contain genes with homology to viral proteins. They are the largest and most complex DNA transposons known. Mavericks are one of the long-sought vectors of horizontal gene transfer. They are related to giant viruses and virophages.

Mavericks are an ancient and fragmented class of jumping genes prevalent in the genomes of protists, fungi and animals, including humans. These massive mobile elements were initially assumed to be inactive, mutated relics of obsolete genes. But later research revealed that Mavericks can be reactivated, and that they can mediate horizontal gene transfer between some species of protists. Complete, intact Mavericks had never been characterized in a multicellular organism.

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