One major “ick factor” of genetic engineering is taking genes from one species and adding them to another species. While it sounds strange, we are all wearing the same genes. It’s not something to be afraid of – in fact, as we learn more it becomes more and more amazing.
Look at the genome of any organism on the planet and you’ll find at least some genes in common with other organisms. The root of this idea is evolution itself. People, dinosaurs, turtles, pumpkins, and lions – we’re all related!
Since we all have a common ancestor, we have genes in common. One way to look at this is in a phylogenetic tree. Like a tree, phylogeny starts with one trunk that then branches out into smaller and smaller branches. Organisms that are closer together on the tree will have more genes in common.
While the similarities between organisms were originally determined by examining physical characteristics from bones to biochemistry, the advent of genome characterization and later sequencing has allowed us to better understand the similarities.
The Understanding Evolution website (created by the University of California Museum of Paleontology and the National Center for Science Education) has a great tutorial on how to read and create phylogenetic trees.
Whole genome comparison
Another way to look at similarities is to compare whole genomes. According to the Genome News Network, “the genomes of more than 180 organisms have been sequenced since 1995.” This includes humans, mosquitoes, various bacteria, and many more (and they’re even missing a few, such as corn!). The genomic sequences can be aligned based on the similarities of their sequences so we can see how similar the genomes are as wholes.
Chunks of genome may be rearranged, mutated, duplicated, and changed in other ways, but we can still find their similar areas. A comparison between human, chimpanzee, Rhesus monkey, mouse, and chicken are shown in this image (click for a larger version). Many parts of the human genome parts are very similar to parts of the other genomes.
Individual gene comparison
While we can see similarities at the whole genome level, looking at individual genes is useful, too. There are many genes in common across wildly different organisms. Some of them are conserved with amazingly few changes while others have mutated over millennia so we can just barely tell the genes had a common ancestor.
A recent example is that popped up in traditional and social media is farnesene synthase – an enzyme that catalyses the synthesis of farnesene, which is a chemical compound that causes odor. Various forms of farnesene (and the enzyme that makes it) are found in many different organisms, including aphids and apples. In apples, farnesene makes a nice apple smell. In aphids, a slightly different farnesene is an alarm pheromone that tells the aphids to run away because a predator is near.
Rothamsted Research in England took a farnesene synthase gene and inserted it into the wheat genome with the goal of scaring aphids away. They also used a farnesyl pyrophosphate synthase gene, with the goal of increasing expression of farnesene (because farnesyl pyrophosphate is a precursor of farnesene). As one of the researchers, Gia Aradottir, described in an interview with Biofortified, both genes were actually synthesized in a lab. The farnesene synthase gene was most similar to the peppermint version of the gene while the farnesyl pyrophosphate synthase gene was most similar to the gene found in mammals, with one tiny sequence particularly similar to the cow version of the gene.
What all this means is that these genes appear in many different types of organisms with minor differences. These homologous genes have a common ancestor, just as the organisms that the genes appear in have a common ancestor. It’s not scary once you understand what’s happening, and it’s clear that the wheat hasn’t been turned into mint or into a cow due to the addition of these genes.
Gene movement between species
Not only do we all have a lot of genes in common, there’s also natural movement between species. My favorite example is fungus genes that produce carotenoids that were borrowed by aphids. The colorful pigment contributed by the fungal genes helps the aphids be less interesting to some of their potential predators. Another example is moss that has picked up genes from fungi, bacteria, and viruses! Want to learn more? David Tribe collects “Natural GMOs” at his blog – he’s up to 149 examples as of October 2012.
Surely, as more and more genomes are sequenced, we will find more gene swapping. Still, while horizontal gene transfer does happen, it is rare, and there are restrictions. For example, genes very rarely move from eukaryotes (multi-celled organisms) to bacteria even though genes can move more easily from bacteria to eukaryotes.
What does this mean for GMOs?
Nothing, really. Humans moving genes between organisms, especially more related ones, isn’t any special cause for concern. Instead, we have to look at what the gene does.
One way to think about it is sentences in books. If we have a cookbook and a bible and we move a sentence from the cookbook to the bible – does it make the bible a cookbook?
There are already some sentences in the bible that are similar to those in the cookbook, and they have many words in common. Consider: “And you, take wheat and barley, beans and lentils, millet and emmer, and put them into a single vessel and make your bread from them.” This verse is Ezekiel 4:9, the recipe behind Ezekiel Bread.
Adding a sentence doesn’t change any of the other sentences. It just adds more information. It definitely does not transform the bible into a cookbook – just as adding a gene to wheat that is similar to a gene from cows does not turn that wheat into a cow.
I’ll close this post with one of my favorite songs: “My brother the ape” by They Might Be Giants