The laws and terms of cannabis genetics

genetics of plants according to mendel

The basics of genetics according to the laws of Johann Gregor Mendel

Terms : Hybrid, polyhybrid, F1, F2, retro-cross, ibl, genotype ou phenotype are very common terms in the cannabis world, and their meanings are often unknown until we see them for the first time in a packet of seeds. Allele (allelomorphic), recessive, dominan genet or homozygous for others they are just meaningless words. To understand and deepen the subject, let's start with the basic concepts of genetics.

First parental generation

Pure varieties used for breeding are often called by the name P, for example, a Colombian, Afghan or Nepalese variety. If we read P1, it would be the first parental generation.
When two varieties are crossed (P1 x P1), we obtain an F1 hybrid (or First Generation Parental). For example, a Colombian x Afghan would be an F1 hybrid.

If we cross these F1s with each other, we will get an F2 hybrid (second generation offspring). And if we cross F2 again, we'll get F3s, and so on. For example, if we cross our first seeds of Colombia x Afghanica F1 with each other, we will get an F2 hybrid.


An IBL is a stabilized hybrid that is obtained from the F6. They are characterized by the great stability that they show, a good example the famous White Widow, a variety without differentiated phenotypes, all the plants being practically equal with the slight variations that a population can have, that we will be able to obtain with our Colombia by Afghanica after these 6 generations crossing the descendants between them.


A backcross is a hybrid, crossed with one of its two parents. For example, our Colombia x Afghanica: if we cross it again with the Afghanica, we will have a BX1 (Back Cross). If we crossed these BX1s at the Afghanica, we would have BX2s and so on.


A polyhybrid is a cross of two hybrids, like that of Jack Herer.
An S1, is a first generation self-pollination, a female plant pollinated with itself by sex inversion, and is always feminized. The SAD S1 is a good example, both by name and because we know it is the self-pollination of a Black Domina.

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Let's take stock: As we can see, by crossing two varieties, we obtain an F1 hybrid which contains 50% of the genetics of each of them. Our Colombia x Afghan has 50% Colombians and 50% Afghans. Logically this is not a stabilized plant and we can find some specimens with great growth typical of Colombian sativa and others lower and richer in Afghan indica or maybe some inherit beautiful ones. red colors characteristics of Colombia. These are the phenotypes, which are the expressions of the genotype in a certain environment, basically the visual differences that we can see there.

Johann Gregor Mendel geneticist and botanist

Gregor Mendel, an Augustinian Catholic monk and naturalist born in the former Austrian Empire, in his garden at St. Thomas Abbey in Brno (now the Czech Republic) began to take notes on his pea crops. Although his studies were published in 1866, they were rejected and forgotten until 1900, a few years after his death, so he never realized what they would mean in the future. Mendel's laws are the foundation of modern genetics. We have summarized them so that you can understand them very easily:

FIRST LAW: principle of uniformity

Taking yellow peas and a few less usual greens, he started crossing them and found himself faced with the first surprise: all the peas came out yellow and not an intermediate color as he had imagined. Whether the cross was yellow x green or green x yellow, the result was always yellow in the branch of the first generation (F1). This is because yellow is a dominant allele (an allele is each of the genetic variants that determine a trait and can be either dominant or recessive. Don't worry, you will understand by now). He therefore concluded that "by crossing two pure breeds, the offspring will be uniform and dominant.

For the colored characters, it should be noted that Mendel starts with homozygous plants. This means that each pea has two identical forms (alleles) of the gene for this characteristic, either two yellow or two green. The plants of the first generation are all heterozygous. In other words, they have inherited two different alleles (one from each parent). A trait is said to be dominant when it appears in the phenotype and genotype of the first generation. A trait is said to be recessive when it does not appear in the phenotype of the first generation, but is present in the genotype.

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Cannabis genetics, Mendel's laws
First and second laws :
1 - Cross of red flowering peas with white flowering peas (both homozygous for this trait, YY and GG).
2 - Generation F1: all individuals are red because the red allele is dominant and the white is recessive). While the parents were both homozygous (YY and GG respectively), all of F1 is heterozygous (YG).
3 - Generation F2: the red and white shapes show a ratio of 3: 1.

SECOND LAW: independent segregation and disjunction of alleles

Mendel crossed the first F1 generation of yellow peas and in the second F2 generation he observed that one in four peas was green. He then deduced that in this second generation, the recessive green allele which was hidden in the first generation appeared. He found the same thing when he did it with two peas that were differentiated by two or more alleles, with smooth peas with rough ones. In the first generation they were all smooth while in the second generation 25% were rough. He concluded that "by crossing two hybrid breeds, the offspring will be variable and 50% hybrid".

Cannabis genetics, Mendel's laws
Third law :
The Punnett checkerboard of two characteristics (white / brown hair, short / long tail, where “brown” and “short” should be dominant) results in the F2 generation of varying phenotypes in the ratio of 9: 3: 3: 1. (S = short (short), s = long, B = brown, b = white).

THIRD LAW: independent distribution or the combination and transmission of characters

Taking it a step further, he crossed smooth yellow peas, with green, rough peas. All the peas obtained in the first generation F1 were yellow and smooth, satisfactory

Now let's translate this as our Colombia x Afghanistan. Let's say the Colombian is red and the Afghan is green. On our first ride in F1, we could see that all the plants are green. But in the second generation F2 we will find some red plants. Indeed, the color green is a dominant allele and the color red a recessive allele. If these red specimens are crossed with each other, the F3 hybrids will be predominantly red.

Cannabis genetics, Mendel's laws
The characters studied by Mendel

All of this is very useful when we want to start make our own seeds by following certain criteria and not by relying solely on chance. If for example our Colombia x Afghanica which is a 50/50 hybrid with a sativa phenotype, we want to give it a more indica touch, with a backcross with the Afghan indica, we would get a BX1 hybrid and it would only keep 25% of the Colombian hybrid. If we look back at Afghanistan, the BX2 result would only retain 12,5% ​​of Colombians. If we were to continue, there would be a point where the Colombian genetics would be imperceptible and we would just have Afghan seeds, very stabilized, that is. Everything is a question of combination, of looking at the dominant or recessive traits. Who knows if any of your creations will become as famous as Skunk.

Tags : GeneticSeedHybridStrain
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