Do different cannabis strains affect you in different ways? A DNA expert reveals the science.

Blue Dream. Sour Diesel. Maui Wowie. Chem Dawg.

Visit any dispensary, and you’ll instantly be greeted by a vast spread of different cannabis strains, all promising varying effects, flavors, and ratios of THC and CBD.

Whether you’re being introduced to a new strain or returning to a tried-and-true favorite, you might seek out a certain type to boost your creativity. Or, maybe you want something to help you wind down and veg out in front of the TV. There are even strains out there that allegedly improve performance in the bedroom.

But is the science behind this solid? Dr. Alisha Holloway isn’t so sure. In fact, her research on cannabis strains suggests that some of the varieties being sought out by consumers – Sour Diesel, for instance – may be something completely different than the name on their label.

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GreenState had the opportunity to talk with the scientific expert on comparative genomics at the San Francisco Exploratorium’s AfterDark event on Cannabis. Her lecture primarily focused on unlocking the genetic mysteries of cannabis as she shared an interactive 3D visualization of the world’s largest genetic database of cannabis varieties, known as the Phylos Galaxy.

“There’s a little bit of clinical and pre-clinical trial work that’s been done to test effects of mostly THC and CBD on medical patients,” Holloway said. “But a lot of the work is in very small sample sizes. I think that we have a really long way to go before we can understand it, and figure out how we can actually increase levels of terpenes and cannabinoids to achieve a desired effect for patient and consumers.”

Terpenes are the compounds that give cannabis plants their smell, flavor, and more generally, the promised effects. Cannabinoids are a type of terpene that specifically occur in cannabis. As it stands, according to Holloway, cannabis isn’t really working in the way it’s intended for medical patients, consumers or growers. But, due to her ongoing research with the Phylos Galaxy, it’s likely that we’ll be able to get there in years to come.

“We can start to apply all of the modern agricultural methods that we have to select a natural variation in the plant, and furthermore, those precise levels of cannabinoids and terpenes,” she said.

But how do we get there? For starters, researchers need to have solid data on the chemical properties of the plant. They also need to know the plant’s phenotype and genotype, or its physical properties and genetic information, respectively.

Basically, phenotypes are the observable physical characteristics of a plant: how much it yields, how tall it is, and how long it takes to flower. There’s also differences in shape and size – cannabis comes in extremely tall, reedy varieties or smaller, bushy varieties.

What Holloway and other researchers want to figure out is whether that wide variation in phenotype is reflected in the cannabis plant’s underlying genetics – or if it’s the way plants are being grown that’s generating diversity. Just as people develop a certain eye or hair color based on genetics, the physical characteristics of different strains of cannabis are based on its genotype and environment.

“I want to know whether the genetic component is really driving this difference, and if we can use that knowledge to breed strains of cannabis that do very specific things,” Holloway said.

That’s where the Phylos Galaxy comes in. The publicly accessible map – you can actually go look at it right now from your Internet browser – shows thousands of samples of strains and their relations to one another. People from all over the world send in samples of their strains for DNA testing – Sour Diesel, for example. Holloway describes the strain as easy to identify because of its fuel-like smell, yellow leaves and thin leaflets.

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“But really, when you go out to a dispensary and see that they have Sour Diesel, it’s not clear that you’re actually getting what you think you’re getting,” Holloway said.

She says she has the data to back up her claim. When the team of researchers looked at all of the samples that had been submitted to them under the name Sour Diesel, they discovered that only about 50 percent of the samples fell into a genetically identical clone group.The rest were all over the map, so to speak. In many cases, some weren’t even related to Sour Diesel.

“Part of the reason we developed the Phylos Galaxy was to really help clarify what is in dispensaries and what people have, and we’re really starting to shed light on the variation that’s out there,” Holloway said. The Galaxy is also helping scientists learn what the closest relatives are to a certain strain, how unique it is, and how many variants there are.

“It’s really the first time ever that anyone’s had the ability to go in and understand what they’re growing,” she said.

The next step of Holloway’s research is to compare each strain’s genome, or its set of chromosomes, with a plant genome that scientists are already familiar with, such as tomatoes, corn or wheat.

By rigorously collecting this data, growers and scientists can not only breed plants faster, but also figure out how to allow them to work in the way they’re intended for medical patients and recreational users.

“This is a really exciting time to be in cannabis, because all of these modern agricultural tools were developed around a decade ago. Now, we can use the ‘tool set’ and apply it to a cannabis plant, which has a lot of diversity. Then, we can use genetics to actually make the strains we want,” Holloway said.

Want to test it out yourself? Learn how to identify your own marijuana genotypes here.

Have comments on this story or questions about cannabis? Send inquiries and tips to amanda.bartlett@sfchronicle.com