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.Once pure breeding lines have been established, plant breedersclassify and statistically analyze the offspring to determine thepatterns of inheritance for that trait.This is the system used byGregor Mendel to formulate the basic laws of inheritance and aidthe modern breeder in predicting the outcome of crosses,1 - Two pure lines of Cannabis that differ in a particular trait arelocated.2 - These two pure-breeding lines are crossed to pro duce an F1generation.3 - The F1 generation is inbred.4 - The offspring of the F1 and F2 generations are classified withregard to the trait being studied.5 - The results are analyzed statistically.6 - The results are compared to known patterns of inheritance sothe nature of the genes being selected for can be characterized.Fixing TraitsFixing traits (producing homozygous offspring) in Cannabis strains is moredifficult than it is in many other flowering plants.With monoecious strains orhermaphrodites it is possible to fix traits by self-pollinating an individual exhibitingfavorable traits.In this case one plant acts as both mother and father.However,most strains of Cannabis are dioecious, and unless hermaphroditic reactions canbe induced, another parent exhibiting the trait is required to fix the trait.If this isnot possible, the unique individual may be crossed with a plant not exhibiting the trait, inbred in the F1 generation, and selections of parents exhibiting thefavorable trait made from the F2 generation, but this is very difficult.If a trait is needed for development of a dioecious strain it might first bediscovered in a monoecious strain and then fixed through selfing and selectinghomozygous offspring.Dioecious individuals can then be selected from themonoecious population and these individuals crossed to breed out monoecism insubsequent generations.Galoch (1978) indicated that gibberellic acid (GA3) promoted stamen productionwhile indoleacetic acid (IAA), ethrel, and kinetin promoted pistil production inprefloral dioecious Cannabis.Sex alteration has several useful applications.Mostimportantly, if only one parent expressing a desirable trait can be found, it isdifficult to perform a cross unless it happens to be a hermaphrodite plant.Hormones might be used to change the sex of a cutting from the desirable plant,and this cutting used to mate with it.This is most easily accomplished bychanging a pistillate cutting to a staminate (pollen) parent, using a spray of 100ppm gibberellic acid in water each day for five consecutive days.Within twoweeks staminate flowers may appear.Pollen can then be collected for selfingwith the original pistillate parent.Offspring from the cross should also be mostlypistillate since the breeder is selfing for pistillate sexuality.Staminate parentsreversed to pistillate floral production make inferior seed-parents since fewpistillate flowers and seeds are formed.If entire crops could be manipulated early in life to produce all pistillate orstaminate plants, seed production and seedless drug Cannabis production wouldbe greatly facilitated.Sex reversal for breeding can also be accomplished by mutilation and byphotoperiod alteration.A well-rooted, flourishing cutting from the parent plant ispruned back to 25% of its original size and stripped of all its remaining flowers.New growth will appear within a few days, and several flowers of reversed sexualtype often appear.Flowers of the unwanted sex are removed until the cutting isneeded for fertilization.Extremely short light cycles (6-8 hour photoperiod) canalso cause sex reversal.How ever, this process takes longer and is much moredifficult to perform in the field.Genotype and Phenotype RatiosIt must be remembered, in attempting to fix favorable characteristics, that amonohybrid cross gives rise to four possible recombinant genotypes, a dihybridcross gives rise to 16 possible recombinant genotypes, and so forth.Phenotype and genotype ratios are probabilistic.If recessive genes are desiredfor three traits it is not effective to raise only 64 offspring and count on gettingone homozygous recessive individual.To increase the probability of success it is better to raise hundreds of offspring, choosing only the best homozygousrecessive individuals as future parents.All laws of inheritance are based onchance and offspring may not approach predicted ratios until many more havebeen phenotypically characterized and grouped than the theoretical minimums.The genotype of each individual is expressed by a mosaic of thousands of subtleoverlapping traits.It is the sum total of these traits that determines the generalphenotype of an individual [ Pobierz całość w formacie PDF ]
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.Once pure breeding lines have been established, plant breedersclassify and statistically analyze the offspring to determine thepatterns of inheritance for that trait.This is the system used byGregor Mendel to formulate the basic laws of inheritance and aidthe modern breeder in predicting the outcome of crosses,1 - Two pure lines of Cannabis that differ in a particular trait arelocated.2 - These two pure-breeding lines are crossed to pro duce an F1generation.3 - The F1 generation is inbred.4 - The offspring of the F1 and F2 generations are classified withregard to the trait being studied.5 - The results are analyzed statistically.6 - The results are compared to known patterns of inheritance sothe nature of the genes being selected for can be characterized.Fixing TraitsFixing traits (producing homozygous offspring) in Cannabis strains is moredifficult than it is in many other flowering plants.With monoecious strains orhermaphrodites it is possible to fix traits by self-pollinating an individual exhibitingfavorable traits.In this case one plant acts as both mother and father.However,most strains of Cannabis are dioecious, and unless hermaphroditic reactions canbe induced, another parent exhibiting the trait is required to fix the trait.If this isnot possible, the unique individual may be crossed with a plant not exhibiting the trait, inbred in the F1 generation, and selections of parents exhibiting thefavorable trait made from the F2 generation, but this is very difficult.If a trait is needed for development of a dioecious strain it might first bediscovered in a monoecious strain and then fixed through selfing and selectinghomozygous offspring.Dioecious individuals can then be selected from themonoecious population and these individuals crossed to breed out monoecism insubsequent generations.Galoch (1978) indicated that gibberellic acid (GA3) promoted stamen productionwhile indoleacetic acid (IAA), ethrel, and kinetin promoted pistil production inprefloral dioecious Cannabis.Sex alteration has several useful applications.Mostimportantly, if only one parent expressing a desirable trait can be found, it isdifficult to perform a cross unless it happens to be a hermaphrodite plant.Hormones might be used to change the sex of a cutting from the desirable plant,and this cutting used to mate with it.This is most easily accomplished bychanging a pistillate cutting to a staminate (pollen) parent, using a spray of 100ppm gibberellic acid in water each day for five consecutive days.Within twoweeks staminate flowers may appear.Pollen can then be collected for selfingwith the original pistillate parent.Offspring from the cross should also be mostlypistillate since the breeder is selfing for pistillate sexuality.Staminate parentsreversed to pistillate floral production make inferior seed-parents since fewpistillate flowers and seeds are formed.If entire crops could be manipulated early in life to produce all pistillate orstaminate plants, seed production and seedless drug Cannabis production wouldbe greatly facilitated.Sex reversal for breeding can also be accomplished by mutilation and byphotoperiod alteration.A well-rooted, flourishing cutting from the parent plant ispruned back to 25% of its original size and stripped of all its remaining flowers.New growth will appear within a few days, and several flowers of reversed sexualtype often appear.Flowers of the unwanted sex are removed until the cutting isneeded for fertilization.Extremely short light cycles (6-8 hour photoperiod) canalso cause sex reversal.How ever, this process takes longer and is much moredifficult to perform in the field.Genotype and Phenotype RatiosIt must be remembered, in attempting to fix favorable characteristics, that amonohybrid cross gives rise to four possible recombinant genotypes, a dihybridcross gives rise to 16 possible recombinant genotypes, and so forth.Phenotype and genotype ratios are probabilistic.If recessive genes are desiredfor three traits it is not effective to raise only 64 offspring and count on gettingone homozygous recessive individual.To increase the probability of success it is better to raise hundreds of offspring, choosing only the best homozygousrecessive individuals as future parents.All laws of inheritance are based onchance and offspring may not approach predicted ratios until many more havebeen phenotypically characterized and grouped than the theoretical minimums.The genotype of each individual is expressed by a mosaic of thousands of subtleoverlapping traits.It is the sum total of these traits that determines the generalphenotype of an individual [ Pobierz całość w formacie PDF ]