T. Ryan Gregory Genetics

Major contributions to our understanding of genome size.

"Why does an onion need five times more DNA than a human?"

The Story

Since before Watson and Crick worked out the structure of DNA, scientists have been wondering why the amount of genetic material varied so widely – several thousand fold between some species. Original assumptions that more complex or intelligent species would have more genetic material were shown to be completely wrong. In fact, some algae have a longer DNA sequence than humans. And, so scientists struggled with the problem until new breakthroughs in genetic sequencing technology were developed in the 1990s thanks to the race to decode the human genome. The birth of modern genomics made it possible for countless genomes to be examined in unprecedented detail.

For Ryan Gregory, this explosion of technology and interest dovetailed neatly with his university education so that he has become a leader in studying the evolution of DNA amounts in different species. In particular he studies what is sometimes called the “C-value enigma”, the question of why some species have more DNA than others. Rather than trying to understand a single group or species in detail, Gregory practices comparative biology with great success. By sampling the genomes of a whole host of different creatures, ranging from mollusks to spiders to turtles, he has been able to establish some patterns.

For instance, he has found that birds have some of the smallest genomes. He thinks this might be related to the ability to fly. Gregory has hypothesized that flight requires smaller cells and smaller genomes to be able to exchange oxygen effectively. To check his hypothesis he examined one of the most extreme metabolic machines in the flying world: hummingbirds. When he measured the size of their genomes he found that indeed they are the smallest of any bird.

Many other discoveries in comparative biology and DNA analysis have been made by Gregory’s group, and he believes that studying the evolution of DNA in various creatures will keep his self-described "broad interests and short attention span" occupied for years to come.

The Science

The C-Value Enigma is a puzzle that has intrigued and frustrated biologists for more than 60 years. Simply put: why do different species have such widely differing amounts of genetic material?

The rise of  molecular genetics helped scientists delve deeper into the problem, but it wasn’t until the race to sequence the human genome (completed in 2001) that modern genome sequencing technology had advanced sufficiently to address the problem.

In his lab, Ryan Gregory applies techniques from comparative biology to genetic science. By comparing the density of stained cell nuclei from one species to a standard species such as fruitflies, where the size of the genome is known with high confidence, Gregory is able to make accurate estimations of the amount of DNA in the genomes of unstudied species. Using this technique, he has examined many different organisms, including worms, insects, and birds. And through studying so many different kinds of organisms, insights into the evolution of genomes have emerged.

Gregory's work on genome size coincides well with the results of the sequencing of the human genome, which showed that the vast majority of our own genome does not take the form of protein-encoding genes. Much of this non-coding DNA represents genetic elements that are capable of making copies of themselves. In fact the human genome has over 1.5 million copies of just two types of these "transposable elements" compared to just 20,000 protein genes.

And while these elements might not be beneficial to human survival, Gregory compares them to some bacteria living in our bodies - some of which are harmful, some beneficial and many just along for the ride, neither hurting nor benefiting us.

Gregory also collected samples in the Canadian Arctic and found that where an organism lives may impact the size of its genome (or vice versa). Comparing creatures such as crustaceans that lived either in the Arctic or in more temperate regions, he found that the Northern cousins had larger genomes. In fact, in the constant competition to see which creature has the biggest genome, Gregory and his colleagues around the world have found some solid contenders that include an Arctic crustacean, some grasshoppers, and a flower. The human genome, by contrast, is nowhere near either extreme in terms of overall size.

As well, annual plants have smaller genomes than perennial plants. And, organisms with lots of cell division or that need to quickly progress through several life cycle stages have really small genomes. For instance, Gregory cites desert frogs that must reproduce quickly during brief rainy periods as having extremely small genomes. Other amphibians, such as salamanders living in the water, may have genome sizes 100 times larger.

Given the huge diversity of species on the planet, sizing up and understanding the evolution of each organism’s genome is no small task. But, the size of the challenge and the chance to work with countless species actually excites Gregory. At least he’ll never be bored.


The field of genomics is advancing so rapidly that it’s difficult to make predictions that won’t seem quaint even a decade from now. I expect that students who will be in university in 10 years will be exposed to a lot more information about genetics, but they will also face the challenge of getting a handle on knowledge that is continually growing. I imagine that in 10 years, my lab’s research will expand to focus more on analyses of genome sequences, as these are becoming much more readily available.  We will probably focus more attention on individual genomes and their components as well, in addition to continuing our large-scale studies of total genome sizes across thousands of species. There will be no shortage of interesting questions, that’s for certain.

Career Advice

Gregory emphasizes that young scientists should spend less time memorizing facts and details and more time developing the ability to think critically. In other words, to enjoy a lifetime passion in science, finding the right way to ask questions could be more important than knowing answers.  Genome biology is one of the fastest growing fields, and Gregory believes that these days in the life sciences it would be difficult not to find something cool to study. In the next few years, technological improvements will make it easier to study genomes in even greater detail. 

The Person

May 16, 1975
Petrolia, Ontario (grew up in Orillia, Ontario)
Guelph, Ontario
Family Members
  • Wife: Sarah Adamowicz (also faculty at University of Guelph Department of Biology)
  • Son: Evan Gregory
Friendly, enthusiastic, funny, passionate.
Favorite Music
The Tragically Hip, The White Stripes, Sam Roberts, Matthew Good, hard rock and classic rock.
Other Interests
Books (usually science and science fiction), movies, music, video games, camping, tinkering with computers and other electronics, building websites, and developing educational resources. Also dabbles in comedy and enjoys refuting the stereotype of boring and overly serious scientists.
Associate Professor
University of Guelph
  • B.Sc., McMaster University, 1997
  • Ph.D., University of Guelph, 2002
  • NSERC Howard Alper Postdoctoral Prize, NSERC, 2003
  • McMaster Alumni Association Arch Award, 2005
  • American Society of Naturalists Young Investigator Award, 2006
  • Canadian Society of Zoologists Bob Boutilier New Investigator Award, 2007
  • Genetics Society of Canada Robert H. Haynes Young Scientist Award, 2010
Dr. Chris Wood, a professor of biology at McMaster University, gave him his first opportunity to conduct original research as an undergraduate and showed him how to develop a scientific question, plan an experiment, and how best to manage a large and productive research lab. Dr. Paul Hebert, a professor of biology at the University of Guelph, introduced him to the topic of genome size and ensured that he had all the necessary tools and guidance to take on the question of genome size diversity in a major way for his PhD.
Last Updated
May 15, 2020

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