It’s relatively common knowledge that different cannabis strains produce different effects.
Often this can be attributed to other cannabis constituents such as terpenes, but the differences in effects are primarily due to variations in the THC/CBD ratio. The relative concentration of THC and CBD is chemotype dependent.
Yet, what is a chemotype? According to experts, a chemotype is a subgroup within a microorganism or plant species.  Different chemotypes have distinct chemical profile because of the minuscule genetic changes allowing a cannabis plant to produce a peculiar chemical composition.  Our article will discuss these chemotypes and how strain genetics influence THC/CBD ratios.
What is the THC/CBD ratio (1:1)?
In most instances, the THC/CBD ratio (1:1) refers to a cannabis product containing an equal amount of THC and CBD. According to various studies on the topic, many people prefer this THC/CBD ratio because the effects are considered more tolerable. Ultimately, this is because CBD is believed to dampen the psychoactivity and side effects of THC to a certain extent.
How do the strain genetics influence THC/CBD ratios?
Let’s unpack how these strain genetics can influence the THC/CBD ratio. As is the case with most animals and plants, cannabis plants inherit two gene copies, but unlike other plants, the enzymes that turn cannabigerolic acid (CBGA) into tetrahydrocannabinolic acid (THCA) or cannabidiolic acid (CBDA) are ciphered by two uniquely different versions of the same gene.
Due to this, a cannabis plant has two copies of the gene, so that’s why there are three possibilities or three chemotypes. A cannabis plant can have two copies of a gene in one enzyme (E1), it can have one copy of each of the genes (E1&E2), or it can have two copies of a gene in another enzyme (E2). The three THC/CBD ratio strain classifications are discussed under the next heading. 
These are the three chemotypes of cannabis
Every cannabis strain is unique, but by knowing the general chemotype classification, a consumer can know what effect they should expect from a strain. A perfect example is that the CBD dominant (chemotype III) strains won’t be as psychoactive compared to THC dominant strains (chemotype I).
- Chemotype I (hemp): This chemotype is THC dominant which means it has low levels of CBD but high levels of THC. When a strain inherits two copies of the E2 gene, this occurs. It’s believed that most commercial strains belong to this category. A few examples of these strains include Girl Scout Cookies and Blue Dream.
- Chemotype II: This chemotype is balanced with moderate levels of CBD and THC. When a strain gets a copy in each of the E1 and E2 genes, this occurs. Popular examples of balanced strains include Cannatonic and Harlequin.
- Chemotype III: This chemotype is CBD dominant with low THC levels but high levels of CBD. When a strain receives two copies of the gene that makes E1, this chemotype occurs. Charlotte’s Web is one of the most famous strains in this category.
Why are THC/CBD ratios important?
It is important to know the precise THC/CBD ratio because, depending on the type of product bought, there will be a different biological response of the body depending on the particular strain consumed. For example, a strain with more CBD will produce a clear-headed non-psychoactive effect which helps ease the mind and nerves.
In contrast, a THC dominant ratio produces a significantly higher psychoactive effect, with a pacifying impact on a person’s body or an energizing and euphoric effect depending on the variety, thus the different chemical composition.
 Pacifico, D. et al. Genetics and Marker-assisted Selection of the Chemotype in Cannabis sativa L. Molecular Breeding; (2006).17(3), 257-268. doi: 10.1007/s11032-005-5681-x [Journal impact factor = 3.26] [Times cited = 111]
 Campbell, L. et al. (2020). Cannabinoid Inheritance Relies on Complex Genetic Architecture. Cannabis And Cannabinoid Research, 5(1), 105-116. doi: 10.1089/can.2018.0015 [Journal impact factor = 4.30] [Times cited = 4]