The real IM?; horizontal gene transfer (Introduction)

by David Turell , Tuesday, October 11, 2016, 19:06 (2752 days ago) @ David Turell

Another very good explanatory article about horizontal gene transfer with great graphics:

http://www.the-scientist.com/?articles.view/articleNo/47151/title/Lateral-Gene-Transfer...

The article:

http://www.the-scientist.com/?articles.view/articleNo/47125/title/Bacteria-and-Humans-H...

"Before we understood that DNA was the genetic code, scientists knew that bacteria transferred it between cells. In 1928, 25 years before the structure of DNA was solved, British bacteriologist Frederick Griffith demonstrated that live, nonvirulent bacteria could transform into virulent microbes after being incubated with a heat-killed virulent strain. Fifteen years later, a trio of researchers at the Rockefeller Institute for Medical Research (now Rockefeller University), Oswald Avery, Colin MacLeod, and Maclyn McCarty, demonstrated that this transformation was mediated by DNA. Even dead bacteria, it seemed, could share their genes.

"This DNA-sharing process, known as horizontal or lateral gene transfer (LGT), is now understood to occur by the direct movement of DNA between two organisms. Almost all bacterial genomes show evidence of past LGT events, and the phenomenon is known to have profound effects on microbial biology, from spreading antibiotic resistance genes to creating new pathways for degrading chemicals. But LGT is not limited to bacteria. Scientists now recognize that microbes transfer DNA to the plants, fungi, and animals they infect or reside in, and conversely, human long interspersed elements (LINEs) have been found in bacterial genomes. Moreover, researchers have documented LGT from fungi to insects and from algae to sea slugs. There is reason to believe that any two major groups of organisms—including humans—can share their genetic codes.

***

"Bacteria are a genomically promiscuous bunch. They do not reproduce sexually but are among the most genetically varied species because they are constantly exchanging bits of their genetic code via LGT. Their diversity has allowed them to adapt to every ecological niche on the planet, from deep-sea hydrothermal vents to the frozen lakes of Antarctica, from rock crevices to our own intestines. LGT between bacteria has been categorized as transformation by free DNA (genetic material is released into the environment by bacteria and taken up by living microbes, as in Griffith’s experiment), transduction by viruses, and direct cell-cell transfer through conjugation.

***

"In 2001, the first draft sequence of the human genome was suggested to have 223 LGT-derived regions that were not present in other species’ genomes that had been sequenced at that time.4 Some researchers quickly disputed this number as an overestimate, even suggesting that all of the proposed LGTs were more likely explained through alternative mechanisms such as gene loss or convergent evolution.5 A new analysis published last year by Alastair Crisp of the University of Cambridge and colleagues found more than 130 traces of possible LGT events in the human genome—including the presence of fungal hyaluronan synthases, a fat mass and obesity associated gene (FTO), and the gene responsible for blood types (ABO). But most, if not all, of the identified events predate the human and primate lineages and were identified because the researchers chose to no longer limit the results to LGTs that exist only in humans and not in other animal species.

"In order for a nonhuman gene to appear in the genomes of many people, however, the LGT needs to occur in the germline so that it can be passed to future generations; and it has to confer some benefit to the host."

Comment: It is obvious that evolution can advance with the phenomenon of HGT. It can be debated whether the first cells had this ability or whether it developed later, which brings us back to pre-programming or dabbling by God. This is a very long and interesting article about the research recently performed, but I've out the major evolutionary thrust of the HGT ability.