Flower Power

Question: How many genes do I share with a flower?


Here’s the thing — this was a challenging question for me to answer. The reason for this has nothing to do with my ability (or possibly lack thereof — you be the judge) to provide a scientific answer. It’s a difficult question for me to answer because subjecting people to horrible puns is admittedly a guilty pleasure of mine. So, just imagine all the self-discipline it took for me to title this post something other than Shake, Shake, Shake What You Got in Them Genes. Rapping Master P lyrics may be another guilty pleasure of mine.

If you can still take me seriously as a human, let alone a scientist, I encourage you to stay with me and read this whole post, because I actually love this question. I am fascinated by genetics and I love flowers, so it’s not surprising that using genetics to compare myself to a flower is how I have chosen to spend my Saturday.

The answer to this question varies depending on the exact flower, but I am going to not-so-randomly choose to focus on how similar we are to a daffodil, so we can put this number into context.

Thirty percent of the genes found in a daffodil can be found within humans.

I am going to give you a minute to let that sink in…….

……..

That sounds crazy to you too, right?

I mean, humans can do all sorts of things that flowers simply cannot. Things like thinking, talking, moving, eating cheeseburgers, and, on that note, grilling cheeseburgers.

Need a more technical example of how different we are?

Plants require carbon dioxide to generate energy from sunlight. This is a process called photosynthesis, which produces oxygen as a byproduct. You, on the other hand, require oxygen to generate the energy that drives just about every cellular process in your body. This process is called respiration and produces carbon dioxide as a byproduct*. So, there’s an example of how plants and humans are designed in completely contrasting manners. Yet, we are 30% similar at the genetic level.

*Technically speaking, plants also utilize respiration — although their version doesn’t require oxygen

It sounds crazy, but it actually can all be explained pretty simply (not to mention raise an interesting conversation about commensal interactions). But, before we dive into the nitty gritty details that will help us understand in what ways we are actually similar to plants, want to know how similar we are to a bunch of other random living things?

I am about to do a bit of a fact drop, so hold onto your genes (couldn’t resist — at least it’s not in the title).

At the genetic level, humans are about….

25–35% similar to plants/flowers (generally)
 44% similar to a honey bee
 65% similar to a chicken
 60% similar to a banana
 61% similar to a house fly
 80% similar to a cow
 88% similar to a mouse
 90% similar to a cat***
 98% similar to a chimpanzee

***re: this video

Okay — so now that we have seen how similar we are to some other organisms, maybe being 30% genetically similar to a daffodil isn’t all that crazy. So let’s get back to the daffodil. What does the 30% that we have in common with this cute little flower even mean?

A lot, actually, and in fact there are some pretty important similarities between plants and humans.

We absorb food similarly. Both humans and plants promote environments that support the growth of microbes that can generate nutrients essential to our respective metabolisms. In humans, this environment is the intestine and the essential nutrients that are produced are mainly vitamins, while plants rely on microbes in the soil surrounding their roots to supply them with nitrogen, phosphorous and potassium.

Cool — so that similarity could account for some of our genetic similarity to plants.

But I am sure you want an example you actually care about (or should)

Let’s look at a well-studied and medically relevant example of how plants and humans are similar.

Like humans, plants have highly developed immune systems that are required to fight off infection. Plants also use a lot of the same types of molecules as humans to detect an invading microbe. For instance, both humans and plants use a pretty simple, evolutionarily-conserved mechanism of relying on their ability to distinguish self from non-self. This is called the innate immune system. Because of this similarity, scientists actually study the plant innate immune system in labs as a simpler way to better understand our innate immune systems. These discoveries made in plants are often relevant to humans.

If you’re still reading, you may be wondering any/all of the following: Why choose to compare ourselves to a flower by looking at genetic similarity? What are genes and what is a genome?

What are genes and why are they so important?

First, let’s talk about genes — and why it’s important to understand why they are important (are you getting that this is important yet?). Genes are sequences of DNA that provide instructions for building these incredibly powerful biological tools called proteins. Proteins carry out functions of our body, like breathing. See, important.

Without a specific gene your body can’t make a specific protein and, therefore, cannot perform that specific function.

So, if my genome lacks the gene that is the blueprint for lactase, a protein that is required to break down lactose into glucose and galactose (aka simple sugars), I am probably a person who is lactose intolerant and should really try to avoid milk products unless I enjoy being uncomfortable. Again, important.

We make a ton of proteins and, because of this, we need a ton of genes as instructions. Our collection of these tons of genes is called our genome.

Ok, so now that we understand why genes are so important, I think it’s a little easier to understand why we would consider using them to compare ourselves to other organisms. It’s important to keep in mind that there are obviously a lot of ways to classify beings, but we have been subscribing to phylogenetics, which is the study of relationships among groups of organisms by comparing traits we inherit from our predecessors, since Aristotle was wandering the Earth saying things like,

“No excellent soul is exempt from a mixture of madness.”

Basically, a long time.

What is phylogenetics?

The practice of using phylogenetics to compare organisms has evolved over time, just like the genes it studies. In its infancy, phylogenetics was mainly used to categorize organisms based on observable traits, including shape, size and color. Today, a powerful approach called comparative genomics, which largely depends on computer-based analysis, compares species at the level of the genes that make up their individual genomes.

As I mentioned before, genomes are chock full of genes, each with their own biological purpose, so it’s no surprise that comparisons at this level can provide massive amounts of information regarding biological similarities and differences. With technology that allows us to identify the sequence of every single gene in an organism, we can now use comparative genomics to ask questions like the one posed. Since both the human and daffodil genomes have been sequenced, we can distinguish the shared genes — or those that are present in both genomes — from those that are specific to each organism.

So, where does that leave us?

Ultimately, this is how we can conclude that, at the genetic level, humans are 30% similar to daffodils, as 30% of our genes can also be found in the daffodil genome. From here, scientists can ask a multitude of questions, particularly those with evolutionary and biological implications. I, personally, am thrilled to share 30% of my genetic identity with a flower, because — well — it’s better than sharing 30% of my genes with a cockroach. Excuse me while I research how similar we are to cockroaches.

Sources:

Marks, J. What It Means to Be 98% Chimpanzee: Apes, People, and Their Genes. 2002. University of California Press.

Zimmer, C. Genes Are Us. And Them. National Geographic. 2013.

Pontius, J.U. et al. Initial sequence and comparative analysis of the cat genome. Genome Research. 2007.

Elsik, C.G. et al. The Genome Sequence of Taurine Cattle: A Window to Ruminant Biology and Evolution. Science. 2009.

Marks, J. et al. 98% Chimpanzee and 35% Daffodil — Genetic Nature/Culture: Anthropology and Science Beyond the Two-Culture Divide. University of California Press. 2003.

Choi, H.W. et al. DAMPs, MAMPs, and NAMPs in plant innate immunity. BMC Plant Biology. 2016.

Genomes — NIH, National Human Genome Research Institute

Comparative Genomics — NIH, National Human Genome Research Institute

euGenes: Homologous Genes Summary Table August-2005

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