greenthumper
Student of the Dragon
Found this on another site, its a good read if you need to understand basic genetics. :smokebuds:
Genetics are somewhat difficult to understand at first so it is best if we give you a grounding in some of the breeding concepts mentioned in this chapter. We will start by first explaining what a couple of words mean. These words will appear throughout this chapter so it is best to define them at this point.
Genes: Each of the units of heredity which are transmitted from parent to offspring in gametes, usually as part of a chromosome, and control or determine a single characteristic in the offspring. [There are genes responsible for each feature of your plant to be inherited, for leaf color, stem structure, texture, smell, potency, etc.]
Alleles: Any of a number of alternative forms of one gene. [For example the Gene for purple bud color may have 2 forms, one for purple and one for dark red.]
Homozygous: An individual that has identical alleles at one or more genetic loci, which is not a heterozygote and so breeds true. [Your plant is to be said homozygous for one feature when it carries in its responsible gene pair the same gene twice, which means both genes of the gene pair are equal.]
Heterozygous: An individual having different alleles at one or more genetic loci. [Your plant is said to be heterozygous for one feature when the genes of the responsible gene pair are unequal.]
Phenotype: An organism distinguishable from others by observable features. [How your plant looks is the phenotype. It is the summary of all the features you can see on the outside of your plant. It can also be smell and taste.]
Genotype: The genetic constitution of an individual, esp. as distinguished from the phenotype; the whole of the genes in an individual or group. [How your plant looks like inside, which features it can possibly inherit -you can't see those -is called the genotype. It is the summary of all genetic information which your plant carries and can inherit to its offspring.]
Dominant: Of a gene or allele: expressed even when inherited from only one parent. Of a hereditary trait: controlled by such a gene; appearing in an individual to the exclusion of its allelic counterpart, when alleles for both are present. [A gene is said to be dominant when its effect can be seen in the phenotype of your plant. Only one dominant allele in the gene pair must be present to be seen in the phenotype of your plant].
Recessive: Of a gene, allele, or hereditary trait: perceptibly expressed only in homozygotes, being masked in heterozygotes by a dominant allele or trait. [A gene is called recessive when its effect can not be seen in the phenotype of your plant, when only one allele is present. The same allele must be present twice in the gene pair if you can see its expression in the phenotype of your plant.] Locus: A position on a chromosome at which a particular gene is located.
Chromosome: A threadlike structure of nucleic acids and protein which carries a set of linked genes and occurs singly in prokaryotes and in characteristic numbers, usu. paired, in the cell nuclei of higher organisms.
GENE PAIRS
All of life is made up of a pattern of genes. This pattern is similar to the two sides of the zip on your jacket. One side is from the mother, the other is from the father. Each "gene locus", a particular space on that chain, controls one bit of information about the eventual appearance of the plant. Each gene locus contains 2 genes, one from the mother, one from the father. A pair of letters such as BB, Bb, Pp, pp, etc generally notates these. Capital refers to dominant genes while lower case refers to recessive. B can Big bud while b can be smaller bud. This is just an example. The letters refer to a human beings imaginary reference for what a specific gene locus controls. Any letter can be assigned to it. Dominant and Recessive: Individual genes within a locus are said to be either dominant or recessive. This is noted by a capital letter for a dominant gene and a lower case letter for a recessive gene. Dominant genes have a stronger effect and if only one is present, will win over the recessive gene in that locus. For example the B gene means the plant will produce big bud, while the b gene means the plant will produce small bud. Since B is dominant a plant with a Bb genotype will produce Big Bud. The B is dominant over the b. In order for a recessive gene to have an effect, both genes must be recessive, so BB is Big Bud, and Bb is Big Bud, but bb will be small bud. Modifying Genes: By breeding we can determine.. Let's say... what the color of the plant's bud will be, or more importantly, what color the offspring of two plants is going to look like. The final appearance however will be the result of more than one gene locus. Plants may have several color genes for different parts of the plant. A plant's genetic structure is quite complex. Partial Dominance: Now that we have explained the basics of dominant and recessive, you can move on to the next step. Some gene loci in plants have more than two possibilities. These are sometimes referred to as ‘partially dominant genes' and are usually given some type of secondary marker such as B' or B". They work just like dominant and recessives except that there are more than two options. If a gene is dominant over another gene, it will win. Just like a dominant will win a recessive.
HARDY-WEINBERG EQUILIBRIUM
Introduction: An understanding of breeding concepts requires a basic understanding of Hardy-Weinberg's Equilibrium. Breeding depends upon the knowledge of population genetics. To understand the value of the H/W Equilibrium, you may have asked yourself a question like this before... If certain diseases are a dominant trait, then why haven't large sections of the population got this disease? The same question applies to cannabis breeding. If purple bud color is a dominant trait then how come my offspring from the purple bud strain do not have purple buds? Or, I have been selecting Indica mothers and cross breeding them with mostly Indica male plants but I have some Sativa leaves. Why does this happen? Hardy-Weinberg's Equilibrium will help you to understand these questions and there answers. Okay, first of all these questions reflect a very common misconception. That misconception is that the dominant allele of a trait will always have the highest frequency in a population and the recessive allele will always have the lowest frequency. There is no logic behind the idea that a dominant trait should show a tendency to spread over a whole population. Also there is no logic behind the idea that a recessive trait should die out. Gene frequencies can be in high ratios or low ratios no matter how the allele is expressed. The allele can also change, depending on certain conditions. It is the changes in gene frequencies over time that result in different plant characteristics. Hardy-Weinberg Equilibrium will show us whether or not gene frequencies have changed in a population. A population is a group of individuals of the same strain or species, [such as cannabis Indica or cannabis Sativa (species), or Skunk#1 and Master Kush (strains of a species)], in a given area whose members can interbreed with one another. This means that they share a common group of genes. This common group of genes is known as the
GENE POOL.
Each gene pool contains all the alleles for all the traits of all the population. For a step in evolution to occur some of the gene frequencies must change. That is why we have different types of cannabis plants. The gene frequency of an allele refers to the number of times an allele for a particular trait occurs compared to the total number of alleles for that trait. Gene frequency is calculated as follows. The number of a specific type of allele, divided by, The total number of alleles in the gene pool. The Hardy and Weinberg principal describes a theoretical situation in which there is no change in the gene pool. This means that there can be no evolution. For a test example let us consider a population whose gene pool contains the alleles B and b. Assign the letter c to the frequency of the dominant allele B and the letter d to the frequency of the recessive allele b. [In most cases you will find that c and d are actually notated as p and q by convention in science, but for this example we will use c and d.] The sum of all the alleles must equal 100%. So c + d = 1. All the random possible combinations of the members of a population would equal (c x c) + 2cd + (d x d). Which can also be expressed as: (c+d) X (c+d) We will explain this in detail in moment, but it is best to know it for now. The frequencies of B and b will remain unchanged generation after generation if:
1. The population is large enough.
2. There are no mutations.
3. There are no preferences. For example a BB male does not prefer a bb female by its nature.
4. No other outside population exchanges genes with this model.
5. Natural selection must not favor any specific individual.
Let us imagine a pool of genes. 12 are B and 18 are b. Now remember The sum of all the alleles must equal 100%. So this means that the total in this case is 12 + 18 = 30. So 30 is 100%. If we want to find the frequencies of B and b and the genotypic frequencies of B, Bb and b then we will have to apply the standard formula that we have just been shown. f (B) = 12/30 = 0.4 = 40% f (b) = 18/30 = 0.6 = 60% Both add to make 100%. Now we know their ratios. So, c + d = 0.4 + 0.6 = 1 We have proven that c + d must equal 1. Very straightforward, yes. Remember that all the random possible combinations of the members of a population would equal (c x c) + 2cd + (d x d), or (c+d) X (c+d) Then, c + d = 0.4 + 0.6 = 1 And (c x c) + 2cd + (d x d) = BB + Bb + bb = .24 + .48 + .30 = 1 This means that the population can increase in size, but the frequencies of B and b will stay the same. Now, suppose we break the 4th law about not introducing another population into this one. Let us say that we add 4 more b. b + b + b + b enter the pool. This brings our total up to 34 instead of 30. What will the gene and genotypic frequencies be? f (B) = 12/34 = .35 = 35 % f (b) = 22/34 = .65 = 65% f (BB) = .12, f (Bb) = .23 and f (bb) = .42 Oppss, .42 does not equal 1. This means that the Equilibrium law fails if the 4th law is not met. When the new genes entered the pool it resulted in a change of the population's gene frequencies. However if no other populations where introduced then the frequency of .42 would be maintained generation after generation. However we would like to point out that we used a very small pool in the above example. If the pool were much larger then the number of changes, even if one or two new genes jumped in, would be insignificant. You could calculate it, but the change would be on an extremely low level 0.000000000001 of a difference in reality. This is just as basic example to get you started. It may not make complete sense at first but if you read on then it will fall into place. Some of you may be asking the question. How do I know if a trait, such as bud color is Homozygous Dominant (BB), or Heterozygous (Bb) or Homozygous Recessive, (bb)? If you have been given seeds or a clone you may have been told that a trait, such potency is Homozygous Dominant, Heterozygous or Homozygous Recessive. However, you will want to prove this to yourself. Especially if you are going to use that plant in a future breeding plan. You will have to do what is called a Test Cross.
THE TEST CROSS
Determining the phenotype of a plant is fairly straightforward. You look at the plant and you see its phenotype. Determining the genotype can not be done through visible observation alone. The genes themselves are somewhat hidden except for their visible related phenotypes. Again there are three possible genotypes that the plant can create. Let's say golden bud is dominant and silver bud is recessive. Here is the table. Homozygous Dominant: BB = Golden Bud. Heterozygous: Bb = Golden Bud Homozygous Recessive: bb = Silver Bud. (The Golden and Silver bud colors are the phenotype. The b and B are genotype notations.) The reason why Bb is golden and not silver is because B dominates b. Most phenotypes are observed characteristics but some things like bud taste are also phenotypes that can not be observed. If we look at a Mostly Sativa species like a Haze plant we will notice that it is pale green. Now in a population of Haze plants we may notice that one or two out of one hundred maybe dark green and not pale green. This suggests that the dark green color is recessive. We are not totally sure until we have completed the test but the gene frequencies suggest this. We may also notice that the bud is golden on most of the plants so this suggests that the golden bud color is a dominant trait. Some of the buds on only a few of the plants may be silver. This suggests that the silver trait is Recessive (bb in our example). We know that the only genotype that produces the recessive trait is homozygous recessive (bb). So if a plant shows a recessive trait in its phenotype, its genotype is probably homozygous recessive. A plant with a recessive trait always has a homozygous recessive genotype. But this leaves us with a problem. Is the Golden bud or pale green leaf color a Homozygous Dominant (BB) or is it Heterozygous (Bb). So now is the time to perform the Test Cross. Any test cross is a cross of an organism with an unknown dominant genotype (like in our case) with an organism that is homozygous recessive for that same trait. To do this test we need another cannabis plant of the opposite sex that is homozygous recessive (bb) for the same trait. So we will stick with bud color as our example. Hey, we have a few silver bud plants around that we think are recessive. Let's use them and see what happens. We pollinate the female plant (Does not matter if the female is dominant or recessive one), and we get our seeds and plant them. 3 7 months later we see the results. This brings us to the next important rule that we will learn. If any of the offspring from a test cross have the recessive trait, the genotype of the parent with the dominant trait must be Heterozygous. We will explain why in a moment and this will all make sense to you. Also we must mention that we should be talking about a large population here. 1000 plants is a good population to be sure with. 100 plants are good but 20 or less can be dodgy. The more plants we use the more reliable our results will be. In our example, our unknown genotype is either BB or Bb. The Silver genotype is bb. Let's put this information into a mathematical series known as Punnett Squares. We start by first putting in out known genotypes (above). We only do these calculations for 2 parents that will breed. We know that our recessive trait is bb and the other is either BB or Bb, so we use the term B? for the time being. Our next step is to fill in the box with what we can calculate. The first row of offspring Bb and Bb will have the dominant trait of Golden Bud. The ?b and ?b can either be Bb Bb, or bb bb. This will either lead to an offspring that will produce more golden bud (Bb), or silver bud (bb). There are 2 possible outcomes. Let us fill in the 2 possible values of ? and see that this is true. The first possible outcome is where ? = B. This means the all are offspring will have Golden bud. The second possible outcome is where ? = b. This means that some of our offspring will have golden bud (Bb) or Silver bud (bb). The first possibility proves that there is no way we can produce silver bud in the offspring. The second possibility proves that we will have some golden bud and some silver bud. Not only that but we can understand clearly what the frequency will be. Count them! Bb + Bb = 2Bb bb + bb = 2bb 2 out of 4 will have golden bud. 2 out of 4 will have silver bud. Half our offspring will have silver bud! The ration is 50:50. The second possibility tells us a number of things.
(1) Both parents need at least one b trait each for the silver bud to pass on if it is a recessive trait.
(2) If any silver bud is produced in the offspring then the mystery parent B? must be Bb. It can not be BB. Remember: Homozygous Dominant: BB = Golden Bud. Heterozygous: Bb = Golden Bud
Homozygous Recessive: bb = Silver Bud. So if the golden bud parent when crossed with a silver bud parent produced only Golden Bud, then the parent must be Homozygous Dominant for that trait. If the parent produced any silver bud then it must be Heterozygous. The rules are:
1. The plant with the dominant trait is always crossed with an organism with the recessive trait.
2. If ANY offspring show the recessive trait, the unknown genotype is heterozygous
3. If ALL the offspring have the dominant trait, the unknown genotype is homozygous dominant
4. Large numbers are needed for reliable results. And this is your first step into the world of breeding because:
(1) When you breed plants you want to continue a trait. Something that you like to see on your plant or taste with your plant or the height of your plant.
(2) When you want to continue that trait you must know if it is Homozygous Dominant, Heterozygous or Homozygous Recessive.
(3) You can find that out by running a test cross.
So the question may arise -How do I breed for several traits, like taste, smell, vigor and color? Well that is a big question. Maybe to understand more about that we should learn more about Hardy- Weinberg Equilibrium. Hardy-Weinberg Equilibrium Part 2 If we mate two individuals that are heterozygous (e.g., Bb) for a trait what will we find? (Let's make the Punnett square). Look at that. In this group our resulting offspring will be: 1 BB, 2 Bb, 1 bb This means that: 25% of their offspring are homozygous for the dominant allele (BB). 50% are heterozygous like their parents (Bb) and 25% are homozygous for the recessive allele (bb). Now look at this closely. Unlike their parents Bb Bb, 25% will express the recessive phenotype bb. So if we where given two parents that displayed golden bud but where BOTH heterozygous for that trait Bb, we would also produce offspring that have silver bud. But since Bb is dominant in both parents, neither of the parents would display the phenotype for silver bud. This is really what breeding is all about. When we have a strain that we want to keep, how do we know that the parts we want to keep will actually be kept in our breeding process? This is where the test cross comes in. If we create seeds from a strain that we bought in a seed-bank how can we be sure that the offspring will have the character that we like? Well the facts are this. If the trait(s) we wish to continue are Homozygous Dominant (BB) in both the parent plants then there is no way we can produce a recessive genotype for that trait in the offspring. We already explained this in the previous section. Let's prove this: Look! It is impossible for the recessive trait to appear. And if both parents contained the recessive trait we can not produce the dominant trait. Let us see this in action too. There we proved that too. So now we are starting to understand that in order to breed a trait properly we must know if it is Homozygous or Heterozygous or Homozygous Recessive before we can understand what it is we are doing and PREDICT THE RESULTS BEFORE THEY HAPPEN. And this ladies and gentlemen is what breeding is all about - Understanding a trait's genotype, predicting the outcome of a cross and LOCKING DOWN TRAITS. So how can we lock down a trait you might ask? Well we will cover this later after we understand a bit more about this subject matter. Gregor Mendel (1822-1884) was an Austrian monk who discovered the basic rules of inheritance by analyzing results from his plant breeding research programs. He noticed that 2 types of Pea plants gave very uniform results when breed within their own gene pool and not with one another. The traits he noticed where: (This is not a Punnett square. Just an example to show the different phenotypes seen in two different Pea plant strains.) He noticed that the offspring all carried the same traits when they breed in with the same population or gene pool. Now since there where no variations in with each strain he guessed that both strains where homozygous for these traits. Because the pea plants where from the same species Mendel guessed that either the Solid seed shells where recessive or the wrinkled seed shells where recessive. So he used the genotype notations (SS for solid, ss for wrinkled). He knew that they could not be Ss, because one lot did not produce any of the other strain's phenotypes when they breed within their own gene pool. Let's explain this via 2 basic Punnett squares where SS = Pea plant#1 for the trait of ‘solid seed shells' and ss = pea plant#2 for the trait of ‘Wrinkled seed shells'. That was Pea plant#1 results. All the offspring will be SS. That was Pea plant#2 results. All the offspring will be ss. The First Hybrid Cross: Mendel made his first hybrid cross between the 2 strains. The results where all solid seeds! Here is the chart below. Now up until this point he did not know which trait from which plant was recessive or dominant. But since all the seeds where solid, then he knew that Pea Plant#1 contained the dominant genotype for seed shape and that Pea Plant#2 contained the recessive genotype for wrinkled seeds. Also he knew that Pea Plant#2 contained the recessive genotype for seed shape. This means that in future TEST CROSSES with other pea strains, he could determine if a seed shape trait is Homozygous or Heterozygous because he had identified the recessive trait (ss). Remember the rules of test crosses to determine this? Here they are again.
1. The plant with the dominant trait is always crossed with an organism with the recessive trait.
2. If ANY offspring show the recessive trait, the unknown genotype is heterozygous
3. If ALL the offspring have the dominant trait, the unknown genotype is homozygous dominant
4. Large numbers are needed for reliable results. So the offspring from the last Punnett square where all Ss. When he crossed 2 parents from the bunch of offspring he got the following results.
What he has done here is to mate 2 individuals that are heterozygous (e.g., Ss) for a seed shape trait. In this group the resulting offspring will be: SS Ss ss This means that: 25% of the offspring are homozygous for the dominant allele (BB). 50% are heterozygous like their parents (Bb) and 25% are homozygous for the recessive allele (bb). Bingo! Remember this a few pages back? In his first cross to create the hybrid plant Mendel ended up with NO recessive traits for seed shape. But when he crossed the offspring because they where heterozygous for that trait he ended up with some having the recessive trait, some having the homozygous trait and some continuing the heterozygous trait. In correct breeding terms his first cross between the plants is called the F1 cross or F1 generation. The breeding out of those offspring is called the F2 cross or F2 generation. Now since he has Ss, ss and SS to work with you can probably do the Punnett square for each to see how they will work out. It would be a good time to test your knowledge on this. Compare your results with what you have learned about ratios in this chapter and you will be able to see how it all fits together. It is really very simple once you know a few rules......but like most things there are exceptions to the rules. Back to frequencies: We know that if two heterozygous parents are crossed that the ratios will be 50/50 with regards to the allele (Remember the genotype can be Ss, SS or ss, but the allele is either S or s. Look at the table below when we cross two heterozygous parents and count the alleles. SS Ss Ss ss We can see S S S S (4 x S) and s s s s (4 x s). If we break them apart we can see this clearly. SS S S (Snap) s s ss Again, we know that if two heterozygous parents are crossed that the ratios will be 50/50 with regards to the allele. Now remember Equilibrium? Where we consider a population with a gene pool that has the sum of all the alleles equal to 100%, but we may have different ratios? Such as 80% have S and 20% have s or 60% have S and 40% have s. Well maybe we should look at where these laws collapse and where they fail to work as expected. There are five reasons when the law of equilibrium fails to work. These are:
1. Mutation
2. Gene migration
3. Genetic drift
4. Non-random mating
5. Natural selection Let us go through each one.
Mutation A mutation is the change in genetic material, which can give rise to heritable variations in the offspring. In nature maybe exposure to radiation will do this. In this case the result will be a mutation of the plants genetic code and thus when it breeds with the same population it is effectively a ‘Migration' of foreign genetic material. Even though nothing new has been added into the population from an outside population, the mutation of one single plant will act just like another strain that migrated into the gene pool. Gene Migration When we deal with a population of plants we refer to a group of plants that breed within themselves without any interference from an outside population. Over time a population will reach equilibrium and this will be maintained as long as no other population migrates to this one. When another population is introduced it will cause new genes to enter the pool. This is called ‘Introgression'. During the process of introgression many new traits will pop up in the population. Genetic Drift: If the population is small equilibrium may be violated. By chance alone certain members will be eliminated from the population. We will find that the frequency of an allele will DRIFT towards higher or lower values. Non-random mating and Natural selection: This suggests that something external may influence a population to a stage where mating is not random. If some flowers develop earlier than others then they will gather pollen earlier than the rest. If some of the males release pollen earlier than others then the mating is not random. Or maybe all males release their pollen earlier resulting in some of the later flowering females ending up as a sinsemilla crop. This means that these late flowering females will not make their contribution to the gene pool. Again equilibrium will not be maintained. With regards to natural selection the environment may cause a problem with a section of plants. If this section does not survive then they will not be able to make a contribution to the gene pool. If this is the case and if selections are made so that other plants do not make a contribution then we know that trait frequencies can be controlled to a certain degree. And the ability to control the frequencies of a trait is what BREEDING IS ALL ABOUT.
HOW TO TRUE BREED A STRAIN
Breeding cannabis strains is all about manipulating gene frequencies. Most strains that are sold by reputable breeders through seed-banks are very uniform in growth. This means the breeder has attempted to lock certain genes down so that the genotypes of those traits are homozygous. If we can imagine for a moment that a breeder has two strains - Master Kush and Silver haze. The breeder lists a few traits that they like. * Donates the trait that they like. This means that they want to create a plant with the following features and call it something like Silver Kush. Now all the genetics that they need are in both of the gene pools for Master Kush and Silver Haze. We could just mix both populations and hope for the best or we could try to save time, space and money by calculating the genotype for each trait and using the results to create a TRUE BREEDING STRAIN (An IBL). The first thing the breeder must do is to understand the genotype of every trait that is featured in his/her ‘ideal' strain. In order to do this the genotype of each parent strain or population for that same trait must be understood. Since there are 4 traits that the breeder is trying to isolate then 4 x 2 = 8 Genotypes for these phenotype expressions must be made known to the breeder. Let us take the Pale Green Leaf of the Silver Haze for starters. The breeder will grow out as many Silver Haze plants as they can find. They will then note down if any of the population have any other leaf color trait. If not, then the breeder will note that the trait is homozygous (We will call the trait -M). Now it can either be MM or mm. If other colored leaves appear in with the population then the breeder must assume that the trait is not homozygous, but heterozygous. If it is heterozygous then we must lock the trait down before we can continue. This is done through selective breeding. Let is look closely at the parents for a moment. If both parents where MM we would not have seen the variations in the population for this trait. It is a locked down trait. We know that this trait will always breed true in its population without any variations. If one of the parents were MM and the other Mm we would have ended up with a 50/50 population of both variations. But one group is clearly homozygous (MM) and the other is heterozygous (Mm). If both where Mm then we would have 25% MM, 50% Mm and 25% mm. Even though we can see the frequencies we still do not know if the Pale green leaf trait is Dominant or Recessive, but we can find this out by performing A Test Cross. Now we are not going to go through the Test Cross chapter again but we can show you how to isolate the genotype that you need, which is either MM or mm because we want to breed that trait true. We must also keep track of the parent plants being used here. To keep parent plants alive, clone them! The exact same genetic material will be passed on from clone to clone. In this this cross do you see MM offspring and the mm offspring? Well by their very nature they can not be the same.
By running several Cross Tests we can isolate the plant that is either MM or mm and break away any Mm from the group. Whether it is MM or mm, we can still breed the trait true by breeding it with other parents that are only MM or mm respectively. So we may have to do several test crosses to find a male and female that have either MM or mm for that trait. Once we have done this we have isolated the genotype and it will breed true within the same population. So if we ran a seed-bank company called PALE GREEN LEAF ONLY BUT EVERYTHING ELSE IS NOT UNIFORM LTD then the seeds that we create will ALL breed PALE GREEN LEAVES and the customer will be happy. In reality though they want the exact same plant that won the cannabis cup last year.....or at least something close to it. So we will have to isolate all the traits that helped that strain of cannabis to win the cup before people are happy with what they are buying. I think you get the point. How many tests it takes to know the genotype is not certain. You may have to use a wide selection of plants to achieve the goal, but never the less it is still achievable and much more so than nonselective breeding in the wild. Each trait must be locked down in a population, so that the population for that trait is homozygous. The next step is to lock down other traits in that same population. Now here is the hard part. When you are working on a trait you must keep the other traits that you are looking for in mind. By breeding alone you may accidentally lock down another trait that you do not want or even remove traits that you want to keep. If this happens then you will just have to work harder at keeping the traits that you want and exploring genotypes through multiple Cross Tests. Eventually through selection and keeping records you will end up with a plant that is true breeding for all the features that you want. The gene pool is there but the objective is to lock down the traits of the pool. Also by keeping your own records you will be building up your own little map of cannabis genes. For instance if someone grows Blueberry from a known breeder and asks what the berry taste genotype is, you might be able to tell them a little bit about your experiences and what you found. This may help them cut corners. Maybe one day we will be able to genetically map cannabis and everything will be much easier. Also a breeder never sits back and says Right! I am going to be on the lookout for all 1000 traits that I want. That is crazy. What they need to do is concentrate on the main phenotypes that will make their plant unique in some way. Once they have locked down 4 or 5 traits they can them move on. Step by step is how True breeding strains are created. If anyone says that they developed a true breeding strain in 1 or 2 years then you can be sure that the genetics they started with where somewhat true breeding in the first place. (Known true breeding strains like Skunk#1 and Afghani#1 have taken 20 years to get to the stage they are at now.) Eventually you will have your Silver Kush strain but only with the 4 genotypes that you wanted to keep. You may still have a variety of non-uniform plants in the group.
Some may have purple stems, others may have green stems, some might be very potent, and others might not be so potent. By constantly selecting new traits that you want to keep, you can manipulate the strain into a totally true breeding strain for every phenotype. However it is extremely unlikely that such a strain exists on the market that is 100% true breeding for every single phenotype. Such a strain would be called ‘A perfect IBL'. If you are able to lock down 90% of the plant's phenotypes in a population then you can claim that your plant is an IBL. I think in today's world that this would be an acceptable % to reach. The core Idea behind this technique is to find what is known as a ‘Donor' plant. A Donor plant is one that contains a true breeding trait (homozygous Dominant) for that trait. The more lock down traits are homozygous Dominant the better are your chances of developing an IBL. IBL is short for In Breed Line. This does not mean that the line of genetics will be true breeding for every trait, but in general this terminology (IBL) used by breeders does refer to a strain as being very uniform in growth for a high % of the strain's phenotypes. Let us use the example of hamsters. In a litter of hamsters we may find that they all have the same phenotypes. If that population reproduces and no other phenotypes crop up then we can consider the fact that these hamsters come from an In Breed Line. If the hamsters continue to breed and all show the same traits without variation then we know for certain that the gene pool has been locked down. There are some breeding techniques that you may like to know about. These techniques can seriously breach the law of Hardy- Weinberg's Equilibrium. Which in our case can be a good thing because it will reduce a trait in a population or promote a trait in a population. The strain MAY not be true breeding for the selected traits, but it will certainly help make the population more uniform for that trait.
Genetics are somewhat difficult to understand at first so it is best if we give you a grounding in some of the breeding concepts mentioned in this chapter. We will start by first explaining what a couple of words mean. These words will appear throughout this chapter so it is best to define them at this point.
Genes: Each of the units of heredity which are transmitted from parent to offspring in gametes, usually as part of a chromosome, and control or determine a single characteristic in the offspring. [There are genes responsible for each feature of your plant to be inherited, for leaf color, stem structure, texture, smell, potency, etc.]
Alleles: Any of a number of alternative forms of one gene. [For example the Gene for purple bud color may have 2 forms, one for purple and one for dark red.]
Homozygous: An individual that has identical alleles at one or more genetic loci, which is not a heterozygote and so breeds true. [Your plant is to be said homozygous for one feature when it carries in its responsible gene pair the same gene twice, which means both genes of the gene pair are equal.]
Heterozygous: An individual having different alleles at one or more genetic loci. [Your plant is said to be heterozygous for one feature when the genes of the responsible gene pair are unequal.]
Phenotype: An organism distinguishable from others by observable features. [How your plant looks is the phenotype. It is the summary of all the features you can see on the outside of your plant. It can also be smell and taste.]
Genotype: The genetic constitution of an individual, esp. as distinguished from the phenotype; the whole of the genes in an individual or group. [How your plant looks like inside, which features it can possibly inherit -you can't see those -is called the genotype. It is the summary of all genetic information which your plant carries and can inherit to its offspring.]
Dominant: Of a gene or allele: expressed even when inherited from only one parent. Of a hereditary trait: controlled by such a gene; appearing in an individual to the exclusion of its allelic counterpart, when alleles for both are present. [A gene is said to be dominant when its effect can be seen in the phenotype of your plant. Only one dominant allele in the gene pair must be present to be seen in the phenotype of your plant].
Recessive: Of a gene, allele, or hereditary trait: perceptibly expressed only in homozygotes, being masked in heterozygotes by a dominant allele or trait. [A gene is called recessive when its effect can not be seen in the phenotype of your plant, when only one allele is present. The same allele must be present twice in the gene pair if you can see its expression in the phenotype of your plant.] Locus: A position on a chromosome at which a particular gene is located.
Chromosome: A threadlike structure of nucleic acids and protein which carries a set of linked genes and occurs singly in prokaryotes and in characteristic numbers, usu. paired, in the cell nuclei of higher organisms.
GENE PAIRS
All of life is made up of a pattern of genes. This pattern is similar to the two sides of the zip on your jacket. One side is from the mother, the other is from the father. Each "gene locus", a particular space on that chain, controls one bit of information about the eventual appearance of the plant. Each gene locus contains 2 genes, one from the mother, one from the father. A pair of letters such as BB, Bb, Pp, pp, etc generally notates these. Capital refers to dominant genes while lower case refers to recessive. B can Big bud while b can be smaller bud. This is just an example. The letters refer to a human beings imaginary reference for what a specific gene locus controls. Any letter can be assigned to it. Dominant and Recessive: Individual genes within a locus are said to be either dominant or recessive. This is noted by a capital letter for a dominant gene and a lower case letter for a recessive gene. Dominant genes have a stronger effect and if only one is present, will win over the recessive gene in that locus. For example the B gene means the plant will produce big bud, while the b gene means the plant will produce small bud. Since B is dominant a plant with a Bb genotype will produce Big Bud. The B is dominant over the b. In order for a recessive gene to have an effect, both genes must be recessive, so BB is Big Bud, and Bb is Big Bud, but bb will be small bud. Modifying Genes: By breeding we can determine.. Let's say... what the color of the plant's bud will be, or more importantly, what color the offspring of two plants is going to look like. The final appearance however will be the result of more than one gene locus. Plants may have several color genes for different parts of the plant. A plant's genetic structure is quite complex. Partial Dominance: Now that we have explained the basics of dominant and recessive, you can move on to the next step. Some gene loci in plants have more than two possibilities. These are sometimes referred to as ‘partially dominant genes' and are usually given some type of secondary marker such as B' or B". They work just like dominant and recessives except that there are more than two options. If a gene is dominant over another gene, it will win. Just like a dominant will win a recessive.
HARDY-WEINBERG EQUILIBRIUM
Introduction: An understanding of breeding concepts requires a basic understanding of Hardy-Weinberg's Equilibrium. Breeding depends upon the knowledge of population genetics. To understand the value of the H/W Equilibrium, you may have asked yourself a question like this before... If certain diseases are a dominant trait, then why haven't large sections of the population got this disease? The same question applies to cannabis breeding. If purple bud color is a dominant trait then how come my offspring from the purple bud strain do not have purple buds? Or, I have been selecting Indica mothers and cross breeding them with mostly Indica male plants but I have some Sativa leaves. Why does this happen? Hardy-Weinberg's Equilibrium will help you to understand these questions and there answers. Okay, first of all these questions reflect a very common misconception. That misconception is that the dominant allele of a trait will always have the highest frequency in a population and the recessive allele will always have the lowest frequency. There is no logic behind the idea that a dominant trait should show a tendency to spread over a whole population. Also there is no logic behind the idea that a recessive trait should die out. Gene frequencies can be in high ratios or low ratios no matter how the allele is expressed. The allele can also change, depending on certain conditions. It is the changes in gene frequencies over time that result in different plant characteristics. Hardy-Weinberg Equilibrium will show us whether or not gene frequencies have changed in a population. A population is a group of individuals of the same strain or species, [such as cannabis Indica or cannabis Sativa (species), or Skunk#1 and Master Kush (strains of a species)], in a given area whose members can interbreed with one another. This means that they share a common group of genes. This common group of genes is known as the
GENE POOL.
Each gene pool contains all the alleles for all the traits of all the population. For a step in evolution to occur some of the gene frequencies must change. That is why we have different types of cannabis plants. The gene frequency of an allele refers to the number of times an allele for a particular trait occurs compared to the total number of alleles for that trait. Gene frequency is calculated as follows. The number of a specific type of allele, divided by, The total number of alleles in the gene pool. The Hardy and Weinberg principal describes a theoretical situation in which there is no change in the gene pool. This means that there can be no evolution. For a test example let us consider a population whose gene pool contains the alleles B and b. Assign the letter c to the frequency of the dominant allele B and the letter d to the frequency of the recessive allele b. [In most cases you will find that c and d are actually notated as p and q by convention in science, but for this example we will use c and d.] The sum of all the alleles must equal 100%. So c + d = 1. All the random possible combinations of the members of a population would equal (c x c) + 2cd + (d x d). Which can also be expressed as: (c+d) X (c+d) We will explain this in detail in moment, but it is best to know it for now. The frequencies of B and b will remain unchanged generation after generation if:
1. The population is large enough.
2. There are no mutations.
3. There are no preferences. For example a BB male does not prefer a bb female by its nature.
4. No other outside population exchanges genes with this model.
5. Natural selection must not favor any specific individual.
Let us imagine a pool of genes. 12 are B and 18 are b. Now remember The sum of all the alleles must equal 100%. So this means that the total in this case is 12 + 18 = 30. So 30 is 100%. If we want to find the frequencies of B and b and the genotypic frequencies of B, Bb and b then we will have to apply the standard formula that we have just been shown. f (B) = 12/30 = 0.4 = 40% f (b) = 18/30 = 0.6 = 60% Both add to make 100%. Now we know their ratios. So, c + d = 0.4 + 0.6 = 1 We have proven that c + d must equal 1. Very straightforward, yes. Remember that all the random possible combinations of the members of a population would equal (c x c) + 2cd + (d x d), or (c+d) X (c+d) Then, c + d = 0.4 + 0.6 = 1 And (c x c) + 2cd + (d x d) = BB + Bb + bb = .24 + .48 + .30 = 1 This means that the population can increase in size, but the frequencies of B and b will stay the same. Now, suppose we break the 4th law about not introducing another population into this one. Let us say that we add 4 more b. b + b + b + b enter the pool. This brings our total up to 34 instead of 30. What will the gene and genotypic frequencies be? f (B) = 12/34 = .35 = 35 % f (b) = 22/34 = .65 = 65% f (BB) = .12, f (Bb) = .23 and f (bb) = .42 Oppss, .42 does not equal 1. This means that the Equilibrium law fails if the 4th law is not met. When the new genes entered the pool it resulted in a change of the population's gene frequencies. However if no other populations where introduced then the frequency of .42 would be maintained generation after generation. However we would like to point out that we used a very small pool in the above example. If the pool were much larger then the number of changes, even if one or two new genes jumped in, would be insignificant. You could calculate it, but the change would be on an extremely low level 0.000000000001 of a difference in reality. This is just as basic example to get you started. It may not make complete sense at first but if you read on then it will fall into place. Some of you may be asking the question. How do I know if a trait, such as bud color is Homozygous Dominant (BB), or Heterozygous (Bb) or Homozygous Recessive, (bb)? If you have been given seeds or a clone you may have been told that a trait, such potency is Homozygous Dominant, Heterozygous or Homozygous Recessive. However, you will want to prove this to yourself. Especially if you are going to use that plant in a future breeding plan. You will have to do what is called a Test Cross.
THE TEST CROSS
Determining the phenotype of a plant is fairly straightforward. You look at the plant and you see its phenotype. Determining the genotype can not be done through visible observation alone. The genes themselves are somewhat hidden except for their visible related phenotypes. Again there are three possible genotypes that the plant can create. Let's say golden bud is dominant and silver bud is recessive. Here is the table. Homozygous Dominant: BB = Golden Bud. Heterozygous: Bb = Golden Bud Homozygous Recessive: bb = Silver Bud. (The Golden and Silver bud colors are the phenotype. The b and B are genotype notations.) The reason why Bb is golden and not silver is because B dominates b. Most phenotypes are observed characteristics but some things like bud taste are also phenotypes that can not be observed. If we look at a Mostly Sativa species like a Haze plant we will notice that it is pale green. Now in a population of Haze plants we may notice that one or two out of one hundred maybe dark green and not pale green. This suggests that the dark green color is recessive. We are not totally sure until we have completed the test but the gene frequencies suggest this. We may also notice that the bud is golden on most of the plants so this suggests that the golden bud color is a dominant trait. Some of the buds on only a few of the plants may be silver. This suggests that the silver trait is Recessive (bb in our example). We know that the only genotype that produces the recessive trait is homozygous recessive (bb). So if a plant shows a recessive trait in its phenotype, its genotype is probably homozygous recessive. A plant with a recessive trait always has a homozygous recessive genotype. But this leaves us with a problem. Is the Golden bud or pale green leaf color a Homozygous Dominant (BB) or is it Heterozygous (Bb). So now is the time to perform the Test Cross. Any test cross is a cross of an organism with an unknown dominant genotype (like in our case) with an organism that is homozygous recessive for that same trait. To do this test we need another cannabis plant of the opposite sex that is homozygous recessive (bb) for the same trait. So we will stick with bud color as our example. Hey, we have a few silver bud plants around that we think are recessive. Let's use them and see what happens. We pollinate the female plant (Does not matter if the female is dominant or recessive one), and we get our seeds and plant them. 3 7 months later we see the results. This brings us to the next important rule that we will learn. If any of the offspring from a test cross have the recessive trait, the genotype of the parent with the dominant trait must be Heterozygous. We will explain why in a moment and this will all make sense to you. Also we must mention that we should be talking about a large population here. 1000 plants is a good population to be sure with. 100 plants are good but 20 or less can be dodgy. The more plants we use the more reliable our results will be. In our example, our unknown genotype is either BB or Bb. The Silver genotype is bb. Let's put this information into a mathematical series known as Punnett Squares. We start by first putting in out known genotypes (above). We only do these calculations for 2 parents that will breed. We know that our recessive trait is bb and the other is either BB or Bb, so we use the term B? for the time being. Our next step is to fill in the box with what we can calculate. The first row of offspring Bb and Bb will have the dominant trait of Golden Bud. The ?b and ?b can either be Bb Bb, or bb bb. This will either lead to an offspring that will produce more golden bud (Bb), or silver bud (bb). There are 2 possible outcomes. Let us fill in the 2 possible values of ? and see that this is true. The first possible outcome is where ? = B. This means the all are offspring will have Golden bud. The second possible outcome is where ? = b. This means that some of our offspring will have golden bud (Bb) or Silver bud (bb). The first possibility proves that there is no way we can produce silver bud in the offspring. The second possibility proves that we will have some golden bud and some silver bud. Not only that but we can understand clearly what the frequency will be. Count them! Bb + Bb = 2Bb bb + bb = 2bb 2 out of 4 will have golden bud. 2 out of 4 will have silver bud. Half our offspring will have silver bud! The ration is 50:50. The second possibility tells us a number of things.
(1) Both parents need at least one b trait each for the silver bud to pass on if it is a recessive trait.
(2) If any silver bud is produced in the offspring then the mystery parent B? must be Bb. It can not be BB. Remember: Homozygous Dominant: BB = Golden Bud. Heterozygous: Bb = Golden Bud
Homozygous Recessive: bb = Silver Bud. So if the golden bud parent when crossed with a silver bud parent produced only Golden Bud, then the parent must be Homozygous Dominant for that trait. If the parent produced any silver bud then it must be Heterozygous. The rules are:
1. The plant with the dominant trait is always crossed with an organism with the recessive trait.
2. If ANY offspring show the recessive trait, the unknown genotype is heterozygous
3. If ALL the offspring have the dominant trait, the unknown genotype is homozygous dominant
4. Large numbers are needed for reliable results. And this is your first step into the world of breeding because:
(1) When you breed plants you want to continue a trait. Something that you like to see on your plant or taste with your plant or the height of your plant.
(2) When you want to continue that trait you must know if it is Homozygous Dominant, Heterozygous or Homozygous Recessive.
(3) You can find that out by running a test cross.
So the question may arise -How do I breed for several traits, like taste, smell, vigor and color? Well that is a big question. Maybe to understand more about that we should learn more about Hardy- Weinberg Equilibrium. Hardy-Weinberg Equilibrium Part 2 If we mate two individuals that are heterozygous (e.g., Bb) for a trait what will we find? (Let's make the Punnett square). Look at that. In this group our resulting offspring will be: 1 BB, 2 Bb, 1 bb This means that: 25% of their offspring are homozygous for the dominant allele (BB). 50% are heterozygous like their parents (Bb) and 25% are homozygous for the recessive allele (bb). Now look at this closely. Unlike their parents Bb Bb, 25% will express the recessive phenotype bb. So if we where given two parents that displayed golden bud but where BOTH heterozygous for that trait Bb, we would also produce offspring that have silver bud. But since Bb is dominant in both parents, neither of the parents would display the phenotype for silver bud. This is really what breeding is all about. When we have a strain that we want to keep, how do we know that the parts we want to keep will actually be kept in our breeding process? This is where the test cross comes in. If we create seeds from a strain that we bought in a seed-bank how can we be sure that the offspring will have the character that we like? Well the facts are this. If the trait(s) we wish to continue are Homozygous Dominant (BB) in both the parent plants then there is no way we can produce a recessive genotype for that trait in the offspring. We already explained this in the previous section. Let's prove this: Look! It is impossible for the recessive trait to appear. And if both parents contained the recessive trait we can not produce the dominant trait. Let us see this in action too. There we proved that too. So now we are starting to understand that in order to breed a trait properly we must know if it is Homozygous or Heterozygous or Homozygous Recessive before we can understand what it is we are doing and PREDICT THE RESULTS BEFORE THEY HAPPEN. And this ladies and gentlemen is what breeding is all about - Understanding a trait's genotype, predicting the outcome of a cross and LOCKING DOWN TRAITS. So how can we lock down a trait you might ask? Well we will cover this later after we understand a bit more about this subject matter. Gregor Mendel (1822-1884) was an Austrian monk who discovered the basic rules of inheritance by analyzing results from his plant breeding research programs. He noticed that 2 types of Pea plants gave very uniform results when breed within their own gene pool and not with one another. The traits he noticed where: (This is not a Punnett square. Just an example to show the different phenotypes seen in two different Pea plant strains.) He noticed that the offspring all carried the same traits when they breed in with the same population or gene pool. Now since there where no variations in with each strain he guessed that both strains where homozygous for these traits. Because the pea plants where from the same species Mendel guessed that either the Solid seed shells where recessive or the wrinkled seed shells where recessive. So he used the genotype notations (SS for solid, ss for wrinkled). He knew that they could not be Ss, because one lot did not produce any of the other strain's phenotypes when they breed within their own gene pool. Let's explain this via 2 basic Punnett squares where SS = Pea plant#1 for the trait of ‘solid seed shells' and ss = pea plant#2 for the trait of ‘Wrinkled seed shells'. That was Pea plant#1 results. All the offspring will be SS. That was Pea plant#2 results. All the offspring will be ss. The First Hybrid Cross: Mendel made his first hybrid cross between the 2 strains. The results where all solid seeds! Here is the chart below. Now up until this point he did not know which trait from which plant was recessive or dominant. But since all the seeds where solid, then he knew that Pea Plant#1 contained the dominant genotype for seed shape and that Pea Plant#2 contained the recessive genotype for wrinkled seeds. Also he knew that Pea Plant#2 contained the recessive genotype for seed shape. This means that in future TEST CROSSES with other pea strains, he could determine if a seed shape trait is Homozygous or Heterozygous because he had identified the recessive trait (ss). Remember the rules of test crosses to determine this? Here they are again.
1. The plant with the dominant trait is always crossed with an organism with the recessive trait.
2. If ANY offspring show the recessive trait, the unknown genotype is heterozygous
3. If ALL the offspring have the dominant trait, the unknown genotype is homozygous dominant
4. Large numbers are needed for reliable results. So the offspring from the last Punnett square where all Ss. When he crossed 2 parents from the bunch of offspring he got the following results.
What he has done here is to mate 2 individuals that are heterozygous (e.g., Ss) for a seed shape trait. In this group the resulting offspring will be: SS Ss ss This means that: 25% of the offspring are homozygous for the dominant allele (BB). 50% are heterozygous like their parents (Bb) and 25% are homozygous for the recessive allele (bb). Bingo! Remember this a few pages back? In his first cross to create the hybrid plant Mendel ended up with NO recessive traits for seed shape. But when he crossed the offspring because they where heterozygous for that trait he ended up with some having the recessive trait, some having the homozygous trait and some continuing the heterozygous trait. In correct breeding terms his first cross between the plants is called the F1 cross or F1 generation. The breeding out of those offspring is called the F2 cross or F2 generation. Now since he has Ss, ss and SS to work with you can probably do the Punnett square for each to see how they will work out. It would be a good time to test your knowledge on this. Compare your results with what you have learned about ratios in this chapter and you will be able to see how it all fits together. It is really very simple once you know a few rules......but like most things there are exceptions to the rules. Back to frequencies: We know that if two heterozygous parents are crossed that the ratios will be 50/50 with regards to the allele (Remember the genotype can be Ss, SS or ss, but the allele is either S or s. Look at the table below when we cross two heterozygous parents and count the alleles. SS Ss Ss ss We can see S S S S (4 x S) and s s s s (4 x s). If we break them apart we can see this clearly. SS S S (Snap) s s ss Again, we know that if two heterozygous parents are crossed that the ratios will be 50/50 with regards to the allele. Now remember Equilibrium? Where we consider a population with a gene pool that has the sum of all the alleles equal to 100%, but we may have different ratios? Such as 80% have S and 20% have s or 60% have S and 40% have s. Well maybe we should look at where these laws collapse and where they fail to work as expected. There are five reasons when the law of equilibrium fails to work. These are:
1. Mutation
2. Gene migration
3. Genetic drift
4. Non-random mating
5. Natural selection Let us go through each one.
Mutation A mutation is the change in genetic material, which can give rise to heritable variations in the offspring. In nature maybe exposure to radiation will do this. In this case the result will be a mutation of the plants genetic code and thus when it breeds with the same population it is effectively a ‘Migration' of foreign genetic material. Even though nothing new has been added into the population from an outside population, the mutation of one single plant will act just like another strain that migrated into the gene pool. Gene Migration When we deal with a population of plants we refer to a group of plants that breed within themselves without any interference from an outside population. Over time a population will reach equilibrium and this will be maintained as long as no other population migrates to this one. When another population is introduced it will cause new genes to enter the pool. This is called ‘Introgression'. During the process of introgression many new traits will pop up in the population. Genetic Drift: If the population is small equilibrium may be violated. By chance alone certain members will be eliminated from the population. We will find that the frequency of an allele will DRIFT towards higher or lower values. Non-random mating and Natural selection: This suggests that something external may influence a population to a stage where mating is not random. If some flowers develop earlier than others then they will gather pollen earlier than the rest. If some of the males release pollen earlier than others then the mating is not random. Or maybe all males release their pollen earlier resulting in some of the later flowering females ending up as a sinsemilla crop. This means that these late flowering females will not make their contribution to the gene pool. Again equilibrium will not be maintained. With regards to natural selection the environment may cause a problem with a section of plants. If this section does not survive then they will not be able to make a contribution to the gene pool. If this is the case and if selections are made so that other plants do not make a contribution then we know that trait frequencies can be controlled to a certain degree. And the ability to control the frequencies of a trait is what BREEDING IS ALL ABOUT.
HOW TO TRUE BREED A STRAIN
Breeding cannabis strains is all about manipulating gene frequencies. Most strains that are sold by reputable breeders through seed-banks are very uniform in growth. This means the breeder has attempted to lock certain genes down so that the genotypes of those traits are homozygous. If we can imagine for a moment that a breeder has two strains - Master Kush and Silver haze. The breeder lists a few traits that they like. * Donates the trait that they like. This means that they want to create a plant with the following features and call it something like Silver Kush. Now all the genetics that they need are in both of the gene pools for Master Kush and Silver Haze. We could just mix both populations and hope for the best or we could try to save time, space and money by calculating the genotype for each trait and using the results to create a TRUE BREEDING STRAIN (An IBL). The first thing the breeder must do is to understand the genotype of every trait that is featured in his/her ‘ideal' strain. In order to do this the genotype of each parent strain or population for that same trait must be understood. Since there are 4 traits that the breeder is trying to isolate then 4 x 2 = 8 Genotypes for these phenotype expressions must be made known to the breeder. Let us take the Pale Green Leaf of the Silver Haze for starters. The breeder will grow out as many Silver Haze plants as they can find. They will then note down if any of the population have any other leaf color trait. If not, then the breeder will note that the trait is homozygous (We will call the trait -M). Now it can either be MM or mm. If other colored leaves appear in with the population then the breeder must assume that the trait is not homozygous, but heterozygous. If it is heterozygous then we must lock the trait down before we can continue. This is done through selective breeding. Let is look closely at the parents for a moment. If both parents where MM we would not have seen the variations in the population for this trait. It is a locked down trait. We know that this trait will always breed true in its population without any variations. If one of the parents were MM and the other Mm we would have ended up with a 50/50 population of both variations. But one group is clearly homozygous (MM) and the other is heterozygous (Mm). If both where Mm then we would have 25% MM, 50% Mm and 25% mm. Even though we can see the frequencies we still do not know if the Pale green leaf trait is Dominant or Recessive, but we can find this out by performing A Test Cross. Now we are not going to go through the Test Cross chapter again but we can show you how to isolate the genotype that you need, which is either MM or mm because we want to breed that trait true. We must also keep track of the parent plants being used here. To keep parent plants alive, clone them! The exact same genetic material will be passed on from clone to clone. In this this cross do you see MM offspring and the mm offspring? Well by their very nature they can not be the same.
By running several Cross Tests we can isolate the plant that is either MM or mm and break away any Mm from the group. Whether it is MM or mm, we can still breed the trait true by breeding it with other parents that are only MM or mm respectively. So we may have to do several test crosses to find a male and female that have either MM or mm for that trait. Once we have done this we have isolated the genotype and it will breed true within the same population. So if we ran a seed-bank company called PALE GREEN LEAF ONLY BUT EVERYTHING ELSE IS NOT UNIFORM LTD then the seeds that we create will ALL breed PALE GREEN LEAVES and the customer will be happy. In reality though they want the exact same plant that won the cannabis cup last year.....or at least something close to it. So we will have to isolate all the traits that helped that strain of cannabis to win the cup before people are happy with what they are buying. I think you get the point. How many tests it takes to know the genotype is not certain. You may have to use a wide selection of plants to achieve the goal, but never the less it is still achievable and much more so than nonselective breeding in the wild. Each trait must be locked down in a population, so that the population for that trait is homozygous. The next step is to lock down other traits in that same population. Now here is the hard part. When you are working on a trait you must keep the other traits that you are looking for in mind. By breeding alone you may accidentally lock down another trait that you do not want or even remove traits that you want to keep. If this happens then you will just have to work harder at keeping the traits that you want and exploring genotypes through multiple Cross Tests. Eventually through selection and keeping records you will end up with a plant that is true breeding for all the features that you want. The gene pool is there but the objective is to lock down the traits of the pool. Also by keeping your own records you will be building up your own little map of cannabis genes. For instance if someone grows Blueberry from a known breeder and asks what the berry taste genotype is, you might be able to tell them a little bit about your experiences and what you found. This may help them cut corners. Maybe one day we will be able to genetically map cannabis and everything will be much easier. Also a breeder never sits back and says Right! I am going to be on the lookout for all 1000 traits that I want. That is crazy. What they need to do is concentrate on the main phenotypes that will make their plant unique in some way. Once they have locked down 4 or 5 traits they can them move on. Step by step is how True breeding strains are created. If anyone says that they developed a true breeding strain in 1 or 2 years then you can be sure that the genetics they started with where somewhat true breeding in the first place. (Known true breeding strains like Skunk#1 and Afghani#1 have taken 20 years to get to the stage they are at now.) Eventually you will have your Silver Kush strain but only with the 4 genotypes that you wanted to keep. You may still have a variety of non-uniform plants in the group.
Some may have purple stems, others may have green stems, some might be very potent, and others might not be so potent. By constantly selecting new traits that you want to keep, you can manipulate the strain into a totally true breeding strain for every phenotype. However it is extremely unlikely that such a strain exists on the market that is 100% true breeding for every single phenotype. Such a strain would be called ‘A perfect IBL'. If you are able to lock down 90% of the plant's phenotypes in a population then you can claim that your plant is an IBL. I think in today's world that this would be an acceptable % to reach. The core Idea behind this technique is to find what is known as a ‘Donor' plant. A Donor plant is one that contains a true breeding trait (homozygous Dominant) for that trait. The more lock down traits are homozygous Dominant the better are your chances of developing an IBL. IBL is short for In Breed Line. This does not mean that the line of genetics will be true breeding for every trait, but in general this terminology (IBL) used by breeders does refer to a strain as being very uniform in growth for a high % of the strain's phenotypes. Let us use the example of hamsters. In a litter of hamsters we may find that they all have the same phenotypes. If that population reproduces and no other phenotypes crop up then we can consider the fact that these hamsters come from an In Breed Line. If the hamsters continue to breed and all show the same traits without variation then we know for certain that the gene pool has been locked down. There are some breeding techniques that you may like to know about. These techniques can seriously breach the law of Hardy- Weinberg's Equilibrium. Which in our case can be a good thing because it will reduce a trait in a population or promote a trait in a population. The strain MAY not be true breeding for the selected traits, but it will certainly help make the population more uniform for that trait.
