How Are Different Strains Made? By Crossing Cannabis Genetics

Cannabis genetics help develop new strains

Mixing cannabis genetics is nothing new. In fact, whether sativa or indica dominant, most strains are hybrids. It's a practice that started generations ago when breeders wanted to advance the hardiness of the plants and the potency in the bud.

Today, flowers are crossed so much, it is unlikely you would find many pure strains over hybrids in dispensaries. Today, most breeders integrate cross genetics as a natural occurrence when creating a marijuana strain.

To understand how and why strains are crossed, it's important to know the foundation of what the crossing of cannabis genetics is.

Cross genetics is the deliberate breeding of two different individuals resulting in a genotype that has genetic parts of both its parents. The result, however, has the potential to be a completely different phenotype. The parents' genetics are combined to form a new genetic makeup that exhibits features and qualities of both parents.

Crossing Births, Auto-Flowering

The crossing of cannabis genetics in the past had a small, yet innovative goal. It begins with a vintage plant, Ruderalis. Breeders found Ruderalis to have auto-flowering capabilities. This gave it the ability to grow no matter what type of lighting was used. Ruderalis grew by age. Unfortunately, the strain was weak and the plant grew small. It wasn't a popular strain to smoke.

baby cannabis plant

Its auto-flowering characteristics needed isolation to create a strain with the same capabilities. Breeders created a plan to cross Ruderalis, isolating the auto-flowering trait and introducing a new marijuana strain with a higher potency.

Over the years, breeders focused on aggressively crossing, revising, and stabilizing strains. They continued to cross Ruderalis with stronger, more potent strains slowly transferring the auto-flowering characteristics to new ones. The years of dedication created potent strains with consistent auto-flowering characteristics. This process continued, adding different genotypes as a priority. Breeders were ready to explore.

Today's Genetic Crossing

The main reason a person would want to cross strains is to improve existing strains. It's interesting to see what research and creativity can result in. Once breeders improved the process of crossing strains, innovators searched for new reasons to cross.

Breeders had desires to cross a variety of strains with a certain selection of phenotypes. While some breeders focused on the THC/CBD phenotypes, others fixated on certain colors, bud types, smells, etc. Breeders travel the world searching for different landrace and other strains to cross.


Each strain has a different phenotype because of its parent's genetic interaction. It will be unlikely to achieve the exact strain you're looking for due to unknown characteristics of cannabis. Limited research lacks hundreds of individual pieces of cannabinoid and terpene information, but breeders do have the power to isolate some of marijuana's phenotypes from the minimal information given.

There are certain terpenes known to produce traits like sense, flavor, and other potential benefits. Alpha Bisabolol, for example, has a floral scent. Camphene has an herbal flavor. While an individual phenotype may not dominate when passed on, its characteristics will integrate with the child strain. Seeds with similar terpenes increase the odds of the offspring strain expressing those same terpenes.

cannabis bug

Before crossing, it's important to know what kind of strain and seeds breeders deal with. The result may not be what you planned if stability is not considered.


Stabilizing concerns the variability and predictability found in the offspring of the parent's genotypes. Variability is the range of different phenotypes, whereas predictability is the ratio of phenotypes. When there is an unstable strain, its seeds carry more than one phenotype between two different plants of the same strain, which will display at least two dissimilar phenotypes. A properly-stabilized strain's seeds will all display the same phenotype upon growth. It's important to be educated about seeds and breeding flowers with preferred selections.

Types of Crossing

Crossing is not simply explained as taking two strains and growing them together. Depending on the expected results, what and how a breeder is crossing will have different results.

Incomplete Dominance: This is when two strains with two varying phenotypes cross, resulting in a third, blended phenotype. You can find this example in most marijuana hybrids. A simple example would be crossing a high THC content strain with a low THC strain, leading to a strain exhibiting an average THC content.

Co-Dominance: This is the genetic crossing of strains with two varying phenotypes resulting in a strain with a third phenotype. It shows the same characteristics of the parents; however, the strain takes the characteristics and keeps them separate resulting in two dominant phenotypes. Think of it as taking two strains and grinding them together for one blunt.

True Bleeding: This is crossing a strain, usually a landrace, with a traditional breeder's creation. It will produce consistent offspring with the dominant parent's phenotype, usually the landrace strain. There will be a single trait that will always recur.

Sometimes, the result of two marijuana strains may not be intentional. Maybe one of the strains has more of the characteristics wanted in a plant. Fortunately, there are other ways to get results than standard crossing.

Backcrossing is when breeders take a child strain and cross it with one of its parents. This helps isolate a chosen trait. The more backcrossing, the more the anticipated trait dominates.

While it seems right to keep backcrossing until anticipated results are achieved, it may also result in low-quality strains. Heavy backcrossing may produce corrupt recessive genes in the plant. It also negatively affects the plant's heath, a process referred to as Inbreeding Depression.

Outbreeding helps with Inbreeding Depression. While aiding the recessive gene, a breeder may find themselves with a variety of results. There is also a chance that the corrupt recessive gene will surface.


A geneticist is a person who works with genetics. Cannabis geneticists study what all the chemicals in marijuana actually do and their genetic basis. There are a few geneticists competing with one another, trying to create their own sequence. Regrettably, at the current time, it is unlikely to assemble and reference a genome unless it's a solid inbred strain.

Their goal is to build a better strain of weed. In order to do that, they must break up the current genetic codes of cannabis plants and analyze them. In other circumstances, geneticists would use the overlaps in the code to put their creation together.

Unfortunately, cannabis genomes are naturally full of repeating sequences and geneticists have difficulty determining with certainty which codes overlap. In modern strains, there are as many as 11 copies of the gene that synthesizes THC.

woman with pot leaf

The first attempt to spice and analyze resulted in hundreds of thousands of tiny, impossible-to-read fragments. The last attempt was used with an updated sequencer called the PacBio, which reads fragmented DNA of 53,000 base pairs. The outcome did not create a genome, however, 583 million base pairs were broken down to 18,000 pieces.

With limited research capabilities, cannabis-crossing is not currently accurate. The hope is that scientists and geneticists are able to fully dive into the science of cannabis. Only then will the creation of marijuana strains have a consistent and precise outcome.