News and Best Practices

Cannabis Genetics and Breeding Made Simple

September 3, 2018

When selling cannabis to customers, it’s easy to get inundated with lots of scientific jargon and insider terminologies. We talk about indicas, sativas, hybrids, cannabinoid ratios and terpenes, but how do all of these aspects factor into the seemingly random nature of breeding?

Let’s take a shallow dive into cannabis genetics and simplify how a breeder might understand the process. For our examples, we’ll focus on the two most prominent cannabinoids, THC and CBD. These two compounds are the most prized and therefore the most valuable, and each has its own advantages and disadvantages for recreational customers and medical marijuana patients.

The plant’s DNA produces different types of proteins or enzymes; THC and CBD are in turn produced by one particular type of protein (called “synthase”). Strains that produce higher amounts of THC—such as Durban Poison or Blue Dream—do so because they contain many genes for the THC synthase protein. Strains with higher amounts of CBD contain many genes for the CBD synthase protein.

But higher THC strains don’t usually make a lot of CBD, since the relationship between THC genes and CBD genes is inversely proportional. In other words, the more THC that a plant produces, the less CBD it’ll produce (and vice versa).

The additional THC (or CBD) genes for a high-level strain come from a process called gene duplication, or repeating the genes in the DNA. This is a somewhat random phenomenon that may be responsible for most new genes seen throughout natural history. A plant like cannabis is especially prone to a lot of repeated genes, simply because it can handle them.

Controlling genes

Trying to control genes can be tricky business. We’re talking about tweaking individual molecules at the DNA level. It’s much easier to take advantage of natural processes, which is precisely what breeders do.

Imagine that we want to breed our very own 1:1 THC:CBD plant for patients. To do this, we simply take a high-THC strain and cross it with a high-CBD strain. We produce only four seeds. By probability alone, we should get four plants with the following traits:

  • One with high THC and low CBD
  • Two with the same level of THC and CBD
  • One with low THC and high CBD

So essentially, we should have two 1:1 plants for every high-THC and every high-CBD plant we grew. After we get our test results back, we can keep those 1:1 genetics by simply inbreeding; that is, we take the 1:1 plants and cross them with each other.

“Mr. Soul,” the moniker of the man who bred the world-famous Cindy 99 strain, recommends a cubing process for breeding out undesirable traits. To cube, he advises growers to “breed the ‘son’ of a pollinated mom, then breed the ‘grandson’ with her, and on and on to delete male genetics and preserve the females.”

Although this may sound somewhat shocking, plants are accustomed to inbreeding in this fashion. They’ve evolved in a way that minimizes the negative effects to near-negligible levels.

Within three or four generations of inbreeding the 1:1 plants, we’ll eliminate the high-THC and high-CBD strains. We’ve got a new strain that consistently produces 1:1 plants.

Breeding for other traits

The process we’ve just described works similarly for making strains that consistently produce high-THC or high-CBD plants. We find the ones with the traits we want, inbreed them, then keep the new genetics. For instance, if we want high-CBD plants, we cross the high-CBD strains with one another until we get rid of any high-THC or 1:1 plants. And so on and so forth.

Other traits like high yield, short stalks or purple flowers may also be inherited. Unfortunately, this model works only for certain types of inherited genes. Many of the traits that growers want today, such as terpene production and resistance to pests, drought and so on, may not be inheritable. Much of this is still being figured out by plant geneticists and computational biologists.

The future of cannabis breeding

Currently, several laboratories in the U.S. are constructing genome maps for Cannabis sativa. We’ve long had the DNA sequence for cannabis, but we don’t yet have the genetic map. A map will tell us where the genes are located on the DNA sequence. This is important, because until we have this map, most breeding procedures are just guesswork. We’re relying on trial and error to breed the traits we want, which means wasted seeds and wasted resources.

But with a genetic map, we’ll know which strains to cross to get the traits we want—and we’ll keep those traits in the lineage.

“In the 18 years of my career in computational biology,” said Syngenta’s Keith Allen, speaking during last October’s CannaGrow Expo in Denver, “I haven’t seen a field advance in genetic understanding as quickly as I have with the cannabis plant.”

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By Randy Robinson
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