The Genetics of THC and CBD

The Genetics of THC and CBD

Welcome to part one in our series on the science of cannabis growing and breeding. We’ll be discussing what makes strains different from each other, interesting facts about cannabis growth traits, and how the underlying genetics can be controlled through precise breeding methods. To get started, let’s talk about the genetics of THC and CBD.

​These two molecules are produced by a pair of enzymes that convert cannabigerol, or CBG, into either THC or CBD, depending on which enzyme is present.

These two enzymes are actually made from slightly different versions of the same gene!

It’s the same concept as having different versions, also known as alleles, of the hair color gene. One version gives you blonde hair, while the other version gives you black hair, but it’s still just one gene that controls hair color . The same is true for THC and CBD.

Cannabigerol (CBG) Molecule

Cannabigerol (CBG)

d9-Tetrahydrocannabinol (THC) Molecule

d9-Tetrahydrocannabinol (THC)

Cannabidiol (CBD) Molecule

Cannabidiol (CBD)

Determining Levels of THC and CBD

When a male plant pollinates a female plant to make seeds, those seeds get one copy of each gene from mom and one copy of each gene from dad. If a plant has two copies of the Bt allele , then the plant will basically only produce THC.  Likewise, if the plant has two copies of the Bd allele then the plant will only make CBD. However, if the plant has one copy of the Bt allele and one copy of the Bd allele, then it will have a mix of THC and CBD.

This is why most strains have either high THC, high CBD, or something close to a even ratio with neither cannabinoid becoming much higher than 15% dry weight. If you’re growing cannabis or hemp from seeds, especially if you’re considering doing any breeding projects, this information is essential to set the foundation for the work you’ll be doing. Check out the image below to get an idea of what the different combinations of THC (Bt) and CBD (Bd) alleles look like at the genetic level. 
At Delta Leaf we can identify whether a plant contains the Bt allele, the Bd allele, or both. This saves time and money by identifying the plants you want immediately after germination, instead of waiting months to observe the phenotype. We can also conduct gender identity tests to analyze male vs. female cannabis and hemp plants through detection of the Y-chromosome. Sample collection kits are available here on our website. Please contact us ahead of time if you want to get your plants tested for the Bt or Bd allele so we can discuss the specific requirements of your project.


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