A new study refutes the claim of direct transfer of genes from bacteria to humans

The heads of the Genome Project dropped a bomb in February when they claimed that genes are able to jump from bacteria directly to humans. A new study refutes their claim

By Yanai Ofran

Genes cannot jump, state two studies published in recent weeks, and it seems that this determination turns one of the biggest genetic sensations of recent months into a scientific duck. With the publication of the draft of the Human Genome Project in February, the heads of the project dropped several bombs, which changed fundamental conventions in biology. Among the surprises, the phenomenon of jumping genes stood out, or as the scientists called it - "horizontal transfer of genes".

Evolutionary logic states that most of the genes in any creature are copies of the genes of its ancestors. For example, 98% of the human genome is identical to the gorilla genome and only 2% of new genes make the difference.

Genes found in more ancient ancestors can also be found in humans. Many genes that serve us faithfully were created already at the dawn of evolution and can even be found in the genome of bacteria. The bacteria passed them on to their invertebrate descendants, who passed them on to their primitive vertebrate descendants, who passed them on to mammals, and from there, through the monkeys, to us.

But Genome Project scientists determined in February that according to a preliminary analysis of the first draft of the genome, between 113 and 223 genes entered the human genome non-hereditarily. These genes are also found in bacteria, but not in creatures that are on the evolutionary path that connects us to the bacteria. In invertebrates, for example, the researchers were unable to find these genes.

How, then, did these genes come to us? The researchers offered a provocative explanation. Genes, they hypothesized, could jump from bacteria to mammals.

It has been known for years that bacteria are able to borrow genes from each other. For example, a bacterium that knows how to overcome a certain antibiotic with the help of a unique gene may pass it on not only to its offspring but also to the entire neighborhood. His neighbors, and even they are bacteria of a different species, can sometimes take the gene from him and with its help acquire resistance to antibiotics.

The scientists believed that such a transfer could also occur between bacteria and humans. The problem is that the mechanism that allows genes to jump between two bacteria is quite simple. In many cases, it is enough for a piece of DNA, which carries the gene, to penetrate a bacterium for the bacterium to become resistant and pass on the resistance to all its descendants.

In humans it is more complicated. In order for a person to acquire a certain gene, the gene must be inserted into the sperm cell or egg from which the person develops. But even if a bacterium succeeds in penetrating the ovary or testicles, and transferring a piece of DNA to a sperm or egg, a long series of complex processes must still take place in order for this piece of DNA to be integrated into the genome. And even if the piece succeeds in penetrating the genome, the chance that it will be recognized by the cell as a gene is zero. Therefore, many biologists found it difficult to believe that such a process actually occurs. However, how else can one explain the fact that there are genes found in bacteria and humans, but not in other vertebrates along the way?

As expected, the theory caused a stir. The opponents of genetic engineering were quick to warn. They expressed concern that genetically modified food might encourage the jumping genes. Today you will eat a genetically modified apricot, and tomorrow you will have a defective offspring, which the gene kills

The pest that was introduced into the apricot jumped into its genome.

Christian organizations were also quick to jump on the bandwagon and saw the new finding as a final refutation of the evolutionary theories. They declared that the Genome Project had uncovered evolution in disguise.

But a study published earlier this month in the journal Science showed that the initial analysis of the draft genome was too preliminary. Steven Saltzberg of the Genomic Research Institute in Rockville, Maryland performed a more thorough analysis of the data. With a team of researchers, Salzberg examined the genomes of other animals. A large part of the genes that were suspected to be jumpers were also located by Salzberg's team in organisms that are on the path between us and the bacteria.

It is therefore possible that the jumping genes passed through normal inheritance from the bacteria until they reached us. But even Saltzberg and his partners admitted that only meticulous detective work, which would draw the family tree of each gene and show how it passed from father to son, from an ancient species to a late species, from the bacteria to us, would settle the debate.

Such work was published this week in the journal "Nature." A team of researchers led by Michael Stanhope from the bioinformatics company collected all the information available on the genes of various creatures from around the Internet. From the genes marked by the heads of the genome project as genes that jumped from bacteria to the human genome, the team selected a group of several dozen genes. Careful comparisons of these genes with all genes known to science, aided by sophisticated mathematical methods, provided a clear answer. It is possible to draw a detailed family tree showing how these genes passed from the bacteria to us in the old and banal way - passed down from parent to offspring.

Stanhope's article crept into almost reprimanding tones, for the lack of thoroughness of the analysis that prompted the heads of the genome project to declare the disclosure of the jumping genes. At this point it seems that those who jumped in this story are not the genes.

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