Cannabis Cross-Breeding & Genetics
I tend to monitor the Unanswered Threads so I can assist some of the newer growers, and I recently came across a great question that, frankly, had no short or easy answer and prompted me to post this thread that will hopefully provide some insight into Cannabis Cross-Breeding & Genetics.
First, let me say that I'm not an expert in breeding, but am knowledeable enough to know that actually creating a good, stable, strain of medical cannabis can take years to accomplish and most of us will never be at that level. However, there's no reason we can't all "play" with some breeding as a way to create some new crosses, create our own seeds, preserve some of our favorite genetics, and have fun along the way.
This is NOT a comprehensive guide to breeding, just an overview and explanation of some of the terms.
We're all likely familiar with the two families of Cannabis used for medicinal purposes, including Cannabis Sativa and Cannabis Indica.
Sativas tend to grow taller with narrow, light green leaves and are native to Mexico, Columbia, Africa, Thailand & India. Indicas tend to grow shorter with fat, dark green leaves and they mature quicker and have more resinous flowers than Sativas. Indicas are native to the high northern mountain ranges of the Afghani Hindu Kush, Pakistani Kara Korams, Russian Pamirs and Indian Himalayas.
There are numerous strains of both Sativa and Indica.
A "Hybrid" is created by crossing two DIFFERENT "True-Breeding" strains. A true-breeding strain simply means that the genetics are stabilized so the seeds will carry traits "true" to the strain. A true-breeding strain is either is "Pure-Bred" or a "Stabilized Hybrid".
A Pure-Bred strain is a landrace strain that has only been able to reproduce with other similar strains, so the have almost identical genes.
A Stabilized Hybrid is created by crossing two different strains and then inbreeding the resulting cross for several generations until their traits become stable from generation to generation.
For breeding purposes, the two true-breeding strains to be used as parents are "P1". An “F1” is a seed or plant with two true-breeding parents and is effectively the first generation of the new strain. That being said, a man & woman can have ten children together and some will have brown hair, some will be blond; some will have blue eyes and some brown, some will be tall others short, etc. In other words, while each child can share some of the traits from either parent, it's very difficult to predict the outcome of that F1 generation since it has not been "stabilized".
The breeder will typically take the F1's that express the traits he's after and, by breeding two F1's, an "F2" is created. And, F2's can be bread with other F2's to create F3's, etc. The more generations you bread out, the more difficult it is to predict the resulting genetic traits, and because of this, breeders typically do not go past the F3 generation.
So, what are the odds you can get the qualities you're looking for when cross-breeding?
For F2's, with any specific trait, there's a 50% chance a specific trait will be common to F1, 25% chance it comes from the P1 male and 25% chance it comes from the P1 Female.
However, "Back-Crossing" can significantly improve those odds. When you back-cross F1 with P1, the F2's now have a 50% chance the trait will be from the F1 and 50% chance it will be from the P1 parent it was back-crossed with.
And, it gets even better (albeit, slightly more complicated!) with back-crossing because if you take that F2 back-cross and back-cross it again with P1, one of two things will happen to the F3 generation: either 100% will have the F2 trait OR 100% will have the P1 trait. These are known as an "F3 back-cross squared" and is a great method of ensuring little genetic drift between generations. However, just because you've managed to lock-in the trait you were looking for doesn't mean that other desireable traits weren't lost along the way.
To create an auto-flowering strain, the photo-period plant is crossed with Cannabis Ruderalis. Ruderalis is a low-THC species of Cannabis which is native to Central and Eastern Europe and Russia. Many people consider Ruderalis to be its own species due to its unique traits and phenotypes which distinguish it from Indicas and Sativas, however it is widely debated as to whether or not Ruderalis is actually a sub-species of Sativa.
Ruderalis is a short and stalky plant compared to Sativa and Indica that typically grows to 1 to 2 1/2 feet tall at harvest, with a rugged and shaggy growth pattern that produces wide, light green leaves. The buds from the ruderalis plant tend to be small but still relatively chunky, and are supported by sturdy, thick stems.
What really sets Ruderalis apart is its flowering cycle that is induced according to its maturity instead of being activated by the light schedule, like Indica and Sativa. Modern Ruderalis hybrids usually begin to flower between 21 and 30 days after the seeds have been planted, regardless of the light cycle.
However, this auto-flowering gene is "recessive" so a true photo-period plant crossed with an auto will always produce photos for offspring, BUT they will all have the auto gene. If you cross two of the Auto x Photo crosses, even though they are both photo, because they both have that recessive auto gene, 25% will be auto. If you then cross two of those auto-ing offspring, you'll get 100% auto.
So, getting the photo is easy, but it would take four generations to ensure the auto trait:
1) P1 Generation - One Auto & One Photo
2) F1 - All photo's with auto trait
3) F2 - 25% auto's
4) F3 - Crossing two F2 auto plants ensures auto's for seeds
That's about all I have time for tonight, so I hope this helps answer some questions.
Happy Harvests!
K
I tend to monitor the Unanswered Threads so I can assist some of the newer growers, and I recently came across a great question that, frankly, had no short or easy answer and prompted me to post this thread that will hopefully provide some insight into Cannabis Cross-Breeding & Genetics.
First, let me say that I'm not an expert in breeding, but am knowledeable enough to know that actually creating a good, stable, strain of medical cannabis can take years to accomplish and most of us will never be at that level. However, there's no reason we can't all "play" with some breeding as a way to create some new crosses, create our own seeds, preserve some of our favorite genetics, and have fun along the way.
This is NOT a comprehensive guide to breeding, just an overview and explanation of some of the terms.
We're all likely familiar with the two families of Cannabis used for medicinal purposes, including Cannabis Sativa and Cannabis Indica.
Sativas tend to grow taller with narrow, light green leaves and are native to Mexico, Columbia, Africa, Thailand & India. Indicas tend to grow shorter with fat, dark green leaves and they mature quicker and have more resinous flowers than Sativas. Indicas are native to the high northern mountain ranges of the Afghani Hindu Kush, Pakistani Kara Korams, Russian Pamirs and Indian Himalayas.
There are numerous strains of both Sativa and Indica.
A "Hybrid" is created by crossing two DIFFERENT "True-Breeding" strains. A true-breeding strain simply means that the genetics are stabilized so the seeds will carry traits "true" to the strain. A true-breeding strain is either is "Pure-Bred" or a "Stabilized Hybrid".
A Pure-Bred strain is a landrace strain that has only been able to reproduce with other similar strains, so the have almost identical genes.
A Stabilized Hybrid is created by crossing two different strains and then inbreeding the resulting cross for several generations until their traits become stable from generation to generation.
For breeding purposes, the two true-breeding strains to be used as parents are "P1". An “F1” is a seed or plant with two true-breeding parents and is effectively the first generation of the new strain. That being said, a man & woman can have ten children together and some will have brown hair, some will be blond; some will have blue eyes and some brown, some will be tall others short, etc. In other words, while each child can share some of the traits from either parent, it's very difficult to predict the outcome of that F1 generation since it has not been "stabilized".
The breeder will typically take the F1's that express the traits he's after and, by breeding two F1's, an "F2" is created. And, F2's can be bread with other F2's to create F3's, etc. The more generations you bread out, the more difficult it is to predict the resulting genetic traits, and because of this, breeders typically do not go past the F3 generation.
So, what are the odds you can get the qualities you're looking for when cross-breeding?
For F2's, with any specific trait, there's a 50% chance a specific trait will be common to F1, 25% chance it comes from the P1 male and 25% chance it comes from the P1 Female.
However, "Back-Crossing" can significantly improve those odds. When you back-cross F1 with P1, the F2's now have a 50% chance the trait will be from the F1 and 50% chance it will be from the P1 parent it was back-crossed with.
And, it gets even better (albeit, slightly more complicated!) with back-crossing because if you take that F2 back-cross and back-cross it again with P1, one of two things will happen to the F3 generation: either 100% will have the F2 trait OR 100% will have the P1 trait. These are known as an "F3 back-cross squared" and is a great method of ensuring little genetic drift between generations. However, just because you've managed to lock-in the trait you were looking for doesn't mean that other desireable traits weren't lost along the way.
To create an auto-flowering strain, the photo-period plant is crossed with Cannabis Ruderalis. Ruderalis is a low-THC species of Cannabis which is native to Central and Eastern Europe and Russia. Many people consider Ruderalis to be its own species due to its unique traits and phenotypes which distinguish it from Indicas and Sativas, however it is widely debated as to whether or not Ruderalis is actually a sub-species of Sativa.
Ruderalis is a short and stalky plant compared to Sativa and Indica that typically grows to 1 to 2 1/2 feet tall at harvest, with a rugged and shaggy growth pattern that produces wide, light green leaves. The buds from the ruderalis plant tend to be small but still relatively chunky, and are supported by sturdy, thick stems.
What really sets Ruderalis apart is its flowering cycle that is induced according to its maturity instead of being activated by the light schedule, like Indica and Sativa. Modern Ruderalis hybrids usually begin to flower between 21 and 30 days after the seeds have been planted, regardless of the light cycle.
However, this auto-flowering gene is "recessive" so a true photo-period plant crossed with an auto will always produce photos for offspring, BUT they will all have the auto gene. If you cross two of the Auto x Photo crosses, even though they are both photo, because they both have that recessive auto gene, 25% will be auto. If you then cross two of those auto-ing offspring, you'll get 100% auto.
So, getting the photo is easy, but it would take four generations to ensure the auto trait:
1) P1 Generation - One Auto & One Photo
2) F1 - All photo's with auto trait
3) F2 - 25% auto's
4) F3 - Crossing two F2 auto plants ensures auto's for seeds
That's about all I have time for tonight, so I hope this helps answer some questions.
Happy Harvests!
K
Great primer 
