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Marijuana Botany by Robert Connel Clark
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<blockquote data-quote="cannebosanac" data-source="post: 20026" data-attributes="member: 1357"><p>poglavlje 3a</p><p></p><p><span style="color: green">Chapter 3 - Genetics and Breeding of Cannabis</span> </p><p>The greatest service which can be rendered to any country is to add a useful plant to its culture. </p><p>-Thomas Jefferson </p><p></p><p>Genetics </p><p>Although it is possible to breed Cannabis with limited success without any knowledge of the laws of inheritance, the full potential of diligent breeding, and the line of action most likely to lead to success, is realized by breeders who have mastered a working knowledge of genetics. </p><p>As we know already, all information transmitted from generation to generation must be contained in the pollen of the staminate parent and the ovule of the pistillate parent. Fertilization unites these two sets of genetic information, a seed forms, and a new generation is begun. Both pollen and ovules are known as gametes, and the transmitted units determining the expression of a character are known as genes. Individual plants have two identical sets of </p><p>genes (2n) in every cell except the gametes, which through reduction division have only one set of genes (in). Upon fertilization one set from each parent combines to form a seed (2n). </p><p>In Cannabis, the haploid (in) number of chromosomes is 10 and the diploid (2n) number of chromosomes is 20. Each chromosome contains hundreds of genes, influencing every phase of the growth and development of the plant. </p><p>If cross-pollination of two plants with a shared genetic trait (or self-pollination of a hermaphrodite) results in offspring that all exhibit the same trait, and if all subsequent (inbred) generations also exhibit it, then we say that the strain (i.e., the line of offspring derived from common ancestors) is truebreeding, or breeds true, for that trait. A strain may breed true for one or more traits while varying in other characteristics. For example, the traits of sweet aroma and early maturation may breed true, while offspring vary in size and shape. For a strain to breed true for some trait, both of the gametes forming the offspring must have an identical complement of the genes that influence the expression of that trait. For example, in a strain that breeds true for webbed leaves, any gamete from any parent in that population will contain the gene for webbed leaves, which we will signify with the letter w. Since each gamete carries one-half (in) of the genetic complement of the offspring, it follows that upon fertilization both "leafshape" genes of the (2n) offspring will be w. That is, the offspring, like both parents, are ww. In turn, the offspring also breed true for webbed leaves because they have only w genes to pass on in their gametes. </p><p>On the other hand, when a cross produces offspring that do not breed true (i.e., the offspring do not all resemble their parents) we say the parents have genes that segregate or are hybrid. Just as a strain can breed true for one or more traits, it can also segregate for one or more traits; this is often seen. For example, consider a cross where some of the offspring have webbed leaves and some have normal compound-pinnate leaves. (To continue our </p><p>system of notation we will refer to the gametes of plants with compound-pinnate leaves as W for that trait. Since these two genes both influence leaf shape, we assume that they are related genes, hence the lower-case w and uppercase W notation instead of w for webbed and possibly P for </p><p>pinnate.) Since the gametes of a true-breeding strain must each have the same genes for the given trait, it seems logical that gametes which produce two types of offspring must have genetically different parents. </p><p>Observation of many populations in which offspring differed in appearance from their parents led Mendel to his theory of genetics. If like only sometimes produces like, then what are the rules which govern the outcome of these crosses? Can we use these rules to predict the outcome of </p><p>future crosses? </p><p>Assume that we separate two true-breeding populations of Cannabis, one with webbed and one with compound-pinnate leaf shapes. We know that all the gametes produced by the webbed-leaf parents will contain genes for leaf-shape w and all gametes produced by the compound-pinnate individuals will have W genes for leaf shape. (The offspring may differ in other characteristics, of course.) </p><p></p><p><a href="http://img169.imageshack.us/my.php?image=clipimage002sw0.jpg" target="_blank"><img src="http://img169.imageshack.us/img169/7968/clipimage002sw0.th.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a> </p><p></p><p></p><p><a href="http://img232.imageshack.us/my.php?image=clipimage003ob3.jpg" target="_blank"><img src="http://img232.imageshack.us/img232/6632/clipimage003ob3.th.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p><p></p><p></p><p>If we make a cross with one parent from each of the true-breeding strains, we will find that 100% of the offspring are of the compound-pinnate leaf phenotype. (The expression of a trait in a plant or strain is known as the phenotype.) What happened to the genes for webbed leaves contained in the webbed leaf parent? Since we know that there were just as many w genes as W genes combined in the offspring, the W gene must mask the expression of the w gene. We term the W gene the dominant gene and say that the trait of compound-pinnate leaves is dominant over the recessive trait of webbed leaves. This seems logical since the normal phenotype in Cannabis has compound-pinnate leaves. It must be remembered, however, that many useful traits that breed true are recessive. The true-breeding dominant or recessive condition, WW or ww, is termed the homozygous condition; the segregating hybrid condition wW or Ww is called heterozygous. When we cross two of the F1 (first filial generation) offspring resulting from the initial cross of the P1 (parental generation) we observe two types of offspring. The F2 generation shows a ratio of approximately 3:1, three compound pinnate type-to-one webbed type. It should be remembered that phenotype ratios are theoretical. The real results may vary from the expected ratios, especially in small samples.</p><p>In this case, compound-pinnate leaf is dominant over webbed leaf, so whenever the genes w and W are combined, the dominant trait W will be expressed in the phenotype. In the F2 generation only 25% of the offspring are homozygous for W so only 25% are fixed for W. The w trait is only expressed in the F2 generation and only when two w genes are combined to form a double-recessive, fixing the recessive trait in 25% of the offspring. If compound-pinnate showed incomplete dominance over webbed, the genotypes in this example would remain the same, but the phenotypes in the F1 generation would all be intermediate types resembling both parents and the F2 phenotype ratio would be 1 compound-pinnate :2 intermediate :1 webbed.</p></blockquote><p></p>
[QUOTE="cannebosanac, post: 20026, member: 1357"] poglavlje 3a [COLOR=green]Chapter 3 - Genetics and Breeding of Cannabis[/COLOR] The greatest service which can be rendered to any country is to add a useful plant to its culture. -Thomas Jefferson Genetics Although it is possible to breed Cannabis with limited success without any knowledge of the laws of inheritance, the full potential of diligent breeding, and the line of action most likely to lead to success, is realized by breeders who have mastered a working knowledge of genetics. As we know already, all information transmitted from generation to generation must be contained in the pollen of the staminate parent and the ovule of the pistillate parent. Fertilization unites these two sets of genetic information, a seed forms, and a new generation is begun. Both pollen and ovules are known as gametes, and the transmitted units determining the expression of a character are known as genes. Individual plants have two identical sets of genes (2n) in every cell except the gametes, which through reduction division have only one set of genes (in). Upon fertilization one set from each parent combines to form a seed (2n). In Cannabis, the haploid (in) number of chromosomes is 10 and the diploid (2n) number of chromosomes is 20. Each chromosome contains hundreds of genes, influencing every phase of the growth and development of the plant. If cross-pollination of two plants with a shared genetic trait (or self-pollination of a hermaphrodite) results in offspring that all exhibit the same trait, and if all subsequent (inbred) generations also exhibit it, then we say that the strain (i.e., the line of offspring derived from common ancestors) is truebreeding, or breeds true, for that trait. A strain may breed true for one or more traits while varying in other characteristics. For example, the traits of sweet aroma and early maturation may breed true, while offspring vary in size and shape. For a strain to breed true for some trait, both of the gametes forming the offspring must have an identical complement of the genes that influence the expression of that trait. For example, in a strain that breeds true for webbed leaves, any gamete from any parent in that population will contain the gene for webbed leaves, which we will signify with the letter w. Since each gamete carries one-half (in) of the genetic complement of the offspring, it follows that upon fertilization both "leafshape" genes of the (2n) offspring will be w. That is, the offspring, like both parents, are ww. In turn, the offspring also breed true for webbed leaves because they have only w genes to pass on in their gametes. On the other hand, when a cross produces offspring that do not breed true (i.e., the offspring do not all resemble their parents) we say the parents have genes that segregate or are hybrid. Just as a strain can breed true for one or more traits, it can also segregate for one or more traits; this is often seen. For example, consider a cross where some of the offspring have webbed leaves and some have normal compound-pinnate leaves. (To continue our system of notation we will refer to the gametes of plants with compound-pinnate leaves as W for that trait. Since these two genes both influence leaf shape, we assume that they are related genes, hence the lower-case w and uppercase W notation instead of w for webbed and possibly P for pinnate.) Since the gametes of a true-breeding strain must each have the same genes for the given trait, it seems logical that gametes which produce two types of offspring must have genetically different parents. Observation of many populations in which offspring differed in appearance from their parents led Mendel to his theory of genetics. If like only sometimes produces like, then what are the rules which govern the outcome of these crosses? Can we use these rules to predict the outcome of future crosses? Assume that we separate two true-breeding populations of Cannabis, one with webbed and one with compound-pinnate leaf shapes. We know that all the gametes produced by the webbed-leaf parents will contain genes for leaf-shape w and all gametes produced by the compound-pinnate individuals will have W genes for leaf shape. (The offspring may differ in other characteristics, of course.) [URL="http://img169.imageshack.us/my.php?image=clipimage002sw0.jpg"][IMG]http://img169.imageshack.us/img169/7968/clipimage002sw0.th.jpg[/IMG][/URL] [URL="http://img232.imageshack.us/my.php?image=clipimage003ob3.jpg"][IMG]http://img232.imageshack.us/img232/6632/clipimage003ob3.th.jpg[/IMG][/URL] If we make a cross with one parent from each of the true-breeding strains, we will find that 100% of the offspring are of the compound-pinnate leaf phenotype. (The expression of a trait in a plant or strain is known as the phenotype.) What happened to the genes for webbed leaves contained in the webbed leaf parent? Since we know that there were just as many w genes as W genes combined in the offspring, the W gene must mask the expression of the w gene. We term the W gene the dominant gene and say that the trait of compound-pinnate leaves is dominant over the recessive trait of webbed leaves. This seems logical since the normal phenotype in Cannabis has compound-pinnate leaves. It must be remembered, however, that many useful traits that breed true are recessive. The true-breeding dominant or recessive condition, WW or ww, is termed the homozygous condition; the segregating hybrid condition wW or Ww is called heterozygous. When we cross two of the F1 (first filial generation) offspring resulting from the initial cross of the P1 (parental generation) we observe two types of offspring. The F2 generation shows a ratio of approximately 3:1, three compound pinnate type-to-one webbed type. It should be remembered that phenotype ratios are theoretical. The real results may vary from the expected ratios, especially in small samples. In this case, compound-pinnate leaf is dominant over webbed leaf, so whenever the genes w and W are combined, the dominant trait W will be expressed in the phenotype. In the F2 generation only 25% of the offspring are homozygous for W so only 25% are fixed for W. The w trait is only expressed in the F2 generation and only when two w genes are combined to form a double-recessive, fixing the recessive trait in 25% of the offspring. If compound-pinnate showed incomplete dominance over webbed, the genotypes in this example would remain the same, but the phenotypes in the F1 generation would all be intermediate types resembling both parents and the F2 phenotype ratio would be 1 compound-pinnate :2 intermediate :1 webbed. [/QUOTE]
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