Dominant & Recessive Traits
Some traits are “dominant” and some are “recessive”. This means that your plants can sometimes be carrying “hidden” traits which won’t show up unless you breed together two plants that both carry a copy of the hidden gene.
So for example, you could take two plants that grow green buds, but some of their offspring could produce pink buds. This means that the parents were carrying genes that can make pink buds and this recessive “pink” trait was brought out in their offspring.
Ultra-Quick Rundown of Mendelian Genetics & Inheritance
Knowing a little bit about genetics and inheritance will give you a huge advantage in your breeding program.
The first thing you need to know is that all plants (and animals) get two version of each gene, one from each of their parents. The interaction between the two versions of a gene can have a huge effect on your plant.
Mendelian genetics examines how plants and animals show different phenotypes depending on their genes.
So lets start by looking at dominant and recessive genes. Certain genes have complete dominance, which means they always “take over” if the plant has even one copy of the gene. Recessive genes will only show up in the phenotype if the plant got two copies of the same recessive gene from each of its parents.
The figures below show examples of Mendelian inheritance. This is super-simplified, but could help you get a better understanding of dominant and recessive genes.
Complete Dominance – Let’s say that cannabis plants can have a “red” or “white” version of a gene that controls bud color. The red version is completely dominant, and the white version is recessive. That means that (with these genes) the plant can only shows buds that are either red or white. It doesn’t “mix” them.
Let me give you an example with a diagram. “R” is the dominant gene in the diagram below. What that means is if a plant carries any copy of the “R” (red) gene than the buds will be red. The buds will only be white if the plant gets two copies of the “W” (white) gene. Let’s look at what happens over 3 generations if a plant with two “R” genes is bred with a plant that has two “W” genes.
Mendelian Inheritance Example – Complete Dominance
(1) Parent generation
(2) F1 generation
(3) F2 generation
You can see that the first generation (F1) above would produce only red flowers since all the offspring would get at least one copy of the “R” gene. But if you crossed those F1 plants together, you would get about 3 reds to every 1 white since you’d start getting plants that received two copies of the “W” gene.
But in many cases, genetics are not that simple. Not all genes follow the dominant-recessive pattern. Often it’s not a case of genes being only “on” or “off.” They may interact with each other to form new combinations. And to add to the confusion, certain traits are produced by the interaction of dozens or even hundreds of genes.
Incomplete Dominance – Let’s look at an example where the genes have incomplete dominance over each other. In these cases neither version of a gene is “dominant.” Instead they partially affect each other.
So what does that look like in practice? The next diagram shows an example of incomplete dominance.
Just like the above example, we start with two plants, one with two version of “R” (buds turn red), and the other with two “W” genes (buds turn white).
But this time both genes display “incomplete” dominance – it’s not that the offspring will show just one version or the other, but actually a mix of the two.
This time, when a plant gets one copy of “R” and one copy of “W,” the flowers will actually turn pink.
Neither version of the gene is completely dominant, so they influence each other creating a “mix” of the two versions of the gene.
Mendelian Inheritance Example – Incomplete Dominance
(1) Parent generation
(2) F1 generation
(3) F2 generation
In this case, the first generation above would produce only pink flowers since all offspring would get one version of each gene. But if you crossed those F1 plants together, you would get a 25% chance of getting white or red, and a 50% chance of getting pink flowers.
But so much more can be affected by genes than just the color of cannabis buds. Smell, taste, mental effects and more are all affected greatly by the genetics of a plant.
One of the best ways to discover interesting hidden or recessive genes in your gene pool is to first cross your starting plants, and then cross their offspring together or “backcross” with their parents to see if new traits appear.
Once you’ve identified a trait you’d like to keep, then you can start crossing that plant with other members of its “family” until you’ve figured out which plants you need to breed together for their offspring to always show that particular trait.
Over time, growers can develop a whole “suite” of new traits that can be consistently bred from their genetic stock.
You may enjoy learning more about genetic inheritance. A great tool to help you visualize dominant and recessive traits is the Punnett Square (shown above) to help you predict how a particular plant cross might turn out. There are other inheritance factors, such as non-medelian inheritance and epigenetics, that can also affect how your plants grow.
