|Humans Have Multiple Genomes|
These posts cover a lot of different issues.
They range anywhere from One Man's Junk Gene Is Another Man's Treasure Gene? and Microbial Hermeneutics - 3 to The Human Microbiome Congress, but the gist of these types of posts has been to point out that human genes make up only about 2% of the human microbiome, while microbial genes make up about 98%.
Today let's talk about a new twist, which is that there may be even more uncertainty about our genetic identity:
From biology class to “C.S.I.,” we are told again and again that our genome is at the heart of our identity. Read the sequences in the chromosomes of a single cell, and learn everything about a person’s genetic information — or, as 23andme, a prominent genetic testing company, says on its Web site, “The more you know about your DNA, the more you know about yourself.”(DNA Double Take). That immediately makes we wonder if any people have been falsely convicted or falsely freed because of the scientific assumptions that are now being questioned:
But scientists are discovering that — to a surprising degree — we contain genetic multitudes. Not long ago, researchers had thought it was rare for the cells in a single healthy person to differ genetically in a significant way. But scientists are finding that it’s quite common for an individual to have multiple genomes. Some people, for example, have groups of cells with mutations that are not found in the rest of the body. Some have genomes that came from other people.
Medical researchers aren’t the only scientists interested in our multitudes of personal genomes. So are forensic scientists. When they attempt to identify criminals or murder victims by matching DNA, they want to avoid being misled by the variety of genomes inside a single person.(ibid, "DNA Double Take"). That is all our troubled judiciary needs, thousands of cases up in the air.
Last year, for example, forensic scientists at the Washington State Patrol Crime Laboratory Division described how a saliva sample and a sperm sample from the same suspect in a sexual assault case didn’t match.
Two other studies offer a potential source dynamic for the observations of forensic and medical scientists studying the human genome.
The first one indicates a lot of genetic mutation has taken place in the human genome in recent times:
The human genome has been busy over the past 5,000 years. Human populations have grown exponentially, and new genetic mutations arise with each generation. Humans now have a vast abundance of rare genetic variants in the protein-encoding sections of the genome.(Nature, "Past 5,000 years prolific for changes to human genome"). The second paper indicates that one heavily resisted scientific discovery, which adds context to this picture, is now confirmed:
A team of scientists from the University of Maryland School of Medicine has found the strongest evidence yet that bacteria occasionally transfer their genes into human genomes, finding bacterial DNA sequences in about a third of healthy human genomes.(The Scientist). The variation in the individual human microbiome increases the likelihood of genetic variation within any individual (see e.g. The Human Microbiome Congress and Weekend Rebel Science Excursion - 21).
The trillions of bacteria in our bodies regularly exchange DNA with each other, but the idea that their genes could end up in human DNA has been very controversial.
Although her team has since found several cases of LGT between bacteria and invertebrates, “it’s still difficult to convince people that it may be happening in the human genome,” she said.
Danchin agrees that the results need to be validated but said, “I am personally convinced what they have found by screening the different databases is true. I think LGT happens much more frequently than we imagine but, most of the time, is just not detectable.”
The world of genetics sometimes has controversies raging, however, that is more common everywhere in science at the edge, where new discoveries are made, rather than at the core (see e.g. State Crimes Against Democracy).
Anyway, you might want to consider the Dredd Blog tongue-in-cheek adage about buying stocks in science textbook publishing companies (see e.g. Textbooks Take Another Hit - 2 and The Appendix of Vestigial Textbooks - 4).
Happy Constitution Day!
The next post in this series is here, the previous post in this series is here.