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Cannabis Breeding Basics

Making cannabis seeds and creating a hybrid is a simple process. All it takes is pollen from one cannabis plant to fertilize another, and a seed is made. See Identifing Male and Female Cannabis Plants for more information on identifying male and female cannabis plants. For example, if we cross a Durban male into a Autoflower Skunk female, we get Auto Skunk X Durban seed as a result. The seed made from this cross will inherit the characteristics of both parents, and each seed will be unique in its expression.

Chains of DNA fold together to create chromosomes in every cell of a plant. These structures are responsible for the features of a plant. Its individual expression and character that we perceive is refereed to as a plant Phenotype. Traits may include plant structure, vigor, smell, resistance to pests, etc. In contrast, the Genotype is the the almost imperceivable sum of all the information in the plants genome. This information can only be collected through a full genomic sequencing of the plant and is not readily accessible to the common breeder. Each chain of DNA caries gene pairs, one from each parent that occupy a Locus, a position on the chain. That pair of genes determines the characteristics of that plant as it grows. Each pair of genes is denoted as an uppercase or lowercase letter indicating whether the gene is Dominant or Recessive. A gene is considered dominant if its expression is detectable in a plants phenotype and is considered recessive if it not apparent in the plants expression. For example; The genes responsible for the auto-flower trait found in Ruderalis Cannabis is in our experience always recessive trait and when crossed with a photoperiod variety the F1 seed produced from this hybrid will all be photoperiod plants. This trait in the F1 seed can be denoted as two possibilities Aa or AA. Where uppercase A is the dominant gene of being photoperiod. Only a plant with a pair of recessive genes can express the auto-flower trait. The recessive pair would be written as aa. When an Allele possess a gene pair that are identical (AA) and breeds true in each generation of seed it is said to be Homozygous for that dominant trait. Unequal gene pairs (Aa) responsible for a plants particular features are refereed to as Heterogeneous.

Backcrossing is a easy technique that involves inbreeding an offspring into a parent. Backcrossing greatly increase the chances of a desirable trait occurring in a population but can also narrow the genetic pool and can increase the likelihood of unwanted and unidentified recessive traits. Viral infection and susceptibility can also result from inbreeding.

As a breeder it is not always as obvious which traits are Homogenous or Heterogeneous. This information however is essential in order to select for desirable traits. The Hardy-Weinburg Model Of Genetic Equilibrium provides a framework for determining whether a trait is Homogynous Dominant, Heterogeneous, or homogenous recessive. First we must understand that a dominant allele for a trait will not always have the highest frequency in a population. Left to its wild and natural state, cannabis traits are determined by natural selection as well as thier genetic predispositions. Not all traits we deem desirable are beneficial for its survival outside our symbiotic care. Gene frequencies can occur in small or larger frequencies and even change over time. Because its impossible to quantify all the variables that effect a plants mutation the Hardy-Weinburg model proposes a hypothetical situation in which gene frequencies would remain constant without external influence.

Considering the population as a whole we know that the frequency of dominate traits and recessive traits must equal 100%. The Hardy Weingburg law takes it a step further and assumes that all the random possible combinations of the population would equal the following equation.

Imagine now that we have 1000 seeds of F3 autoflower Skunk x Durban. In that population 420 show the auto-flower characteristics while the remaining 580 are autoflower plants. Lets say we want to breed for the auto-flower trait and in the F2 selection we chose only auto-flower dominant plants to create F3 seed. Using the equation above we can determine that the frequency of the auto-flower gene (AA or Aa) is 42% and the frequency of the allele aa is 58%. If the frequency of aa is .58 we can determine that the frequency of a single recessive gene a x a =.58 so a= .76 Same holds true for the frequency of dominant gene (A) if A+a=100% then the frequency of the auto-flower gene (A) must be .24 or 24%. The frequency of these genes will remain unchanged as long as the population is large enough, there are no mutations, there are no inherent preferences for mating partners, no outside pollination, and natural selection has no effect.

Lets say that by the fourth generation (F4) the entire population of plants are auto-flowers. We can now say that our population is Homogenous Dominant for that characteristic. There are inevitably other characteristics that we would like to breed for as well and its important as a breeder to work multiple desirable attributes as a line of genetics is worked.

Lets say that a small portion of the population has a terpene profile high in limonene that we would like to work on. This trait can only be heterogeneous at this stage in breeding because both homogenous dominant and homogenous recessive genes would be considered true breeding. The limonene rich population is then considered homogenous recessive while the remaining population would be considered heterogeneous or possibly homogenous dominant. A plant that displays a recessive trait in its phenotype always has a homozygous recessive genotype. This leaves the question of whether the limonene rich characteristic is homozygous dominant (AA) or heterogeneous (Aa) in the new population we are selecting from. In order to determine this we have to do a test cross.

Test Crossing is an important tool for determining whether a trait is Homogynous Dominant, Heterogeneous, or homogenous recessive. A test cross is performed by breeding with a dominant genotype (AA or Aa) with a plant that is homogenous recessive for the same trait. In this case the limonene dominant plant would be crossed with a plant that does not have that terpene profile. If any of the offspring of the test cross display the recessive trait the parent with the dominant trait must be heterogeneous and not homozygous. With this knowledge we can determine whether or not we would like to use the parents for further breeding. If the offspring from our dominant genotype all smell like limonene then we know that the dominant parent was homogenous for the limonene trait, and are much closer to our goal of breeding true for that chemovar.

Further advanced breeding techniques can be found in The Cannabis Breeders Bible. <--- Free Download as an academic resource.

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