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Isolated facts in biology/botany texts
Your comment "The present understanding of gene change can be briefly
stated as 'Cut, Copy, Paste.'" refers to transposons, which can cause mutations: http://users.rcn.com/jkimball.ma.ult...ansposons.html http://users.rcn.com/jkimball.ma.ult...Mutations.html Therefore, it seems you are agreeing with my statement that "genes and alleles do arise by chance via mutation." I still don't see how you can disparage one definition of evolution without explaining why and yet will not provide a definition you consider satisfactory. Your statement that the evolution definitions "confuse measurement with definition" is a bogus argument. Measuring a change in allele frequency is not at all like "measuring individual body weight" as you suggest. Human body weight is largely a function of environment, not genetics. I don't see that you have any basis for criticizing the American education system when you can't even provide a definition for evolution. Again, you are still confusing homogeneity and homozygosity. One reason why Coffea arabica is disease susceptible might be its homogeneity but that does not necessarily have anything to do with its homozygosity. A homozygous crop can be very disease resistant if it has the required disease resistance alleles. Too, heterozygous crops are often homogeneous, which increases their disease susceptibility. For example, in 1970, most of the hybrid corn cultivars in the United States had the same genes for Southern corn leaf blight susceptibility resulting in a devastating epidemic for that disease. You stated "As I stated a few posts back you will have to find another source to continue your education on the evolution of plant diseases." If you are implying that I view you as a source of education on evolution of plant diseases, you have proved that false time and time again because you provide no facts or references to support your hypotheses. I mainly end up just pointing out your errors. It appears that you either know very little or don't want to share your vast knowledge because you will not answer any of the questions I have posed, e.g. 1. "What is your definition of evolution if you disagree with the definition I presented, i.e. ."...evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next."" 2. "Based on your contention that "extra genes/alleles have additional effects" how do you explain that C. arabica with 44 chromosomes is more disease susceptible than C. canephora with just 22?" 3. "...your hypothesis that homozygous species or cultivars will be more disease susceptible than heterozygous species and cultivars. Is that just something you thought up yourself or is there a website, book or reference where you got the hypothesis from?" David R. Hershey "P van Rijckevorsel" wrote in message ... David Hershey wrote If chance mutations don't give rise to new alleles in plant species, then how do they arise? Many alleles do not code for "normal" or functional proteins. The explanation is that the abnormal alleles arose via mutations in the existing normal allele. + + + It is a truism that our understanding of how 'nature' works keeps pace with the development in the technology surrounding us. For example human brain functions were once compared with cog-and-gear systems and are now likened to computers. The present understanding of gene change can be briefly stated as "Cut, Copy, Paste" Note that not all genes code for proteins. + + + You stated "Glad to see these two sites contradicting each other, when it comes to (mis)defining evolution ;-) Although it remains sad to see evolution so poorly taught". You cast aspersions on the two evolution websites I cited but give no substantive reasons why you berate them. If you find they contain inaccuracies why not point them out to justify your criticisms? What is your definition of evolution if you disagree with the definition I presented, i.e. ."...evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next."? Notice that the definition does not include natural selection because it is not absolutely required for evolution to occur, although natural selection very often does cause evolution. Allele frequency can change without natural selection due to genetic drift: http://www.talkorigins.org/faqs/genetic-drift.html + + + There are two major things wrong with these "definitions": - firstly they confuse measurement with definition. You can try and measure the progress of evolution by measuring gene / allele change. That is not evolution but only one way of measuring it. It is like expressing human progress over the last millenia by measuring individual body weight: this may be be useful data but presents only a small part of the picture. - secondly it says nothing about evolution: if you replace the word "evolution" by "genetic change" you can put this 'definition' into just about any Creationist textbook without anybody raising an eyebrow I had heard that the American educational system had gone to hell but if this is part of any textbook actually used in schools it is much worse than is usually sketched. I can only hope that the website presents it out of context. + + + You stated, "You also emphatically stated several times that of any one gene only one version was active, at least distinctly implying that you held an alternate theory on why polyploids often have "greater vigor than diploids", since you so heavily discount the obvious explanation that the extra genes / alleles have additional effects." I never said that "of any one gene only one version was active" always occurred. I only said that when you have a heterozygous condition, the recessive allele often codes for no protein. I even gave an example from Mendel's wrinkled/smooth peas. I pointed out last time that Coffea arabica is a tetraploid with 44 chromosomes and C. canephora is a haploid with 22 chromosomes. Based on your contention that "extra genes/alleles have additional effects" how do you explain that C. arabica with 44 chromosomes is more disease susceptible than C. canephora with just 22? + + + Coffea arabica is particular susceptible to a new disease developing since it is a crop that is both homozygote and homogeneous. I assumed you had caught that by now? + + + After all these posts, you still have provided no evidence beyond one example for your hypothesis that homozygous species or cultivars will be more disease susceptible than heterozygous species and cultivars. Is that just something you thought up yourself or is there a website, book or reference where you got the hypothesis from? David R. Hershey + + + As I stated a few posts back you will have to find another source to continue your education on the evolution of plant diseases. PvR =============================== "P van Rijckevorsel" wrote David Hershey wrote Chance is an important part of evolution because genes and alleles do arise by chance via mutation. Your own Hugo de Vries brought the concept of mutation into the Theory of Evolution. Without the genes or alleles provided by mutation, natural selection would have nothing to select for. Even clones, such as apple cultivars, often produce favorable mutations that result in new improved cultivars. + + + Actually there has been progress in science since Hugo de Vries, and it is pretty clear that mutations as such are not really the factor they were made out to be, unless one takes the position that any change in the genome is a mutation, which would be a self-redundant statement. How long it may last till the lay public realizes this is another matter. Creationism certainly does not help. As I have been trying to make clear there is a difference between species and cultivars. The fact that 'mutations' occasionally give rise to new cultivars has little bearing on what happens in species. The common link between species and cultivars are that they arise through selection, but both method and purpose of these respective forms of selection are greatly different. + + + I did say that natural selection was responsible for changing the frequency of alleles and genes. A change in the frequency of a gene or allele in a population results in evolution. It not uncommon to define evolution that way, e.g."...evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next." - http://atheism.about.com/library/glo..._evolution.htm There are also other factors besides natural selection that cause evolution: http://www.ucl.ac.uk/~ucbhdjm/course.../OneGenePP.pdf + + + Glad to see these two sites contradicting each other, when it comes to (mis)defining evolution. ;-) Although it remains sad to see evolution so poorly taught + + + The frequency of an allele often changes due to natural selection. For example, suppose one mutation in one plant gives rise to an allele X providing resistance to an often lethal disease. If that disease occurs widely in the population, then plants with the X allele will survive at a far greater rate than those without allele X. Thus, most plants of the species will eventually carry the X allele so its frequency increases greatly. Stop putting words in my mouth again, I presented no "alternative theory on polyploids". I don't dispute that polyploids often have greater vigor than diploids. However, that tends to contradict your hypothesis given that C. arabica is a tetraploid with 44 chromosomes, and C. canephora is a diploid with 22. + + + You also emphatically stated several times that of any one gene only one version was active, at least distinctly implying that you held an alternate theory on why polyploids often have "greater vigor than diploids", since you so heavily discount the obvious explanation that the extra genes / alleles have additional effects. + + + The key dispute has been your unsupported hypothesis that homogygous crops are more disease susceptible than heterozygous crops simply because they are homozygous. The only example you cite is homozygous Coffea arabica being more susceptible to disease than heterozygous C. canephora. However, that could be due to poor breeding or poor selection of C. arabica cultivars. It could also be that C. arabica by chance simply has fewer disease reistance genes or alleles than C. canephora. You have yet to provide any evidence that the homozygous status of C. arabica has anything to do with is greater disease susceptibility. David R. Hershey + + + Actually the key item was the undesirability of presenting isolated facts in botany texts, such as mentioning that peas are self-pollinated and that peas were used by Mendel, without explaining why self-pollination was essential to Mendel for carrying out his landmark experiments. There are far too many isolated facts and names going about, when it would not be all that much harder to teach concepts. PvR |
#2
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Isolated facts in biology/botany texts
Dear David,
I note you feel you are occupied "just pointing out [my] errors". Although I would readily admit any errors I might have made it would seem I cannot see you actually pointing out any. If I have to describe what it is you are doing it would seem you fasten upon I word I use, you connect this with a random word you derive from an unknown source and off you go ... Since you were kind enough to provide such a clear example I will use that to set the record straight. I stated: "It is like expressing human progress over the last millenia by measuring individual body weight: this may be be useful data but presents only a small part of the picture". If one were to conduct a poll as to what constitutes "human progress over the last millenia" one might get quite different answers, such as the invention of the wheel, the agricultural revolution, the invention of the printing press, the industrial revolution, instant coffee, automobiles, computers, cell-phones, nintendo, etc but genetic change would not be high on the list, perhaps not even in the top thousand. Yet you blithely state "Measuring a change in allele frequency is not at all like "measuring individual body weight" as you suggest. Human body weight is largely a function of environment, not genetics." Although I am sure you will take this the wrong way, I feel honor bound to advise you, with all due respect, to confer with your doctor about your medication. As to gene expression it is clear you are hampered by some severe misconceptions. The safe advice would be for you to refrain from commenting on this topic. This is the more so since it would not be enough for you to read a book on the topic. As I am sure you are aware re-education is much harder than education. You would need to take a course on the topic to straighten matters out, and this might come hard. You had better avoid it. Sorry to be so blunt. sincerely, PvR |
#3
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Isolated facts in biology/botany texts
The human genome project has shown that some human genes originated in
bacteria and have been passed to humans from the bacteria by horizontal transfer. There is no reason to believe that this is unique to humans and has almost certainly happened to many other organisms in other kingdoms as well as humans. This is evolutionary, but does not involve the mutation of any alleles, merely the addition of new (for that organism) alleles. I am not, of course, saying that mutations do not happen, just that there are other ways for the genome of any organism to change possibly leading to selection and thus evolution. John "Don't ask me what I think of you, I might not give the answer you want me to, Oh well." - Peter Green "David Hershey" wrote in message om... If chance mutations don't give rise to new alleles in plant species, then how do they arise? Many alleles do not code for "normal" or functional proteins. The explanation is that the abnormal alleles arose via mutations in the existing normal allele. snip |
#4
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Isolated facts in biology/botany texts
I often cite references to support my scientific facts. You are the
one who almost always relies on an "unknown source" and will not reveal your sources even when asked. You are the one who has gone off on many tangents in this thread, e.g. talking about human genetics and human body weight that have nothing to do with botany. I am just responding to topics that you have brought up such as your homozygous versus heterozygous disease susceptibility hypothesis. I have pointed out many of your errors, e.g. 1. Your incorrect generalization that a homozygous crop will be more disease susceptible than a heterozygous crop. 2. Your harsh criticism of the definition of evolution I quoted, i.e. "...evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next." You are apparently unable to substantiate the criticisms or provide a more accurate definition. 3. Your rejecting the concept that mutation plays an essential role in evolution by stating "it is pretty clear that mutations as such are not really the factor they were made out to be" but then countering that "The present understanding of gene change can be briefly stated as 'Cut, Copy, Paste.'" The "Cut, Copy, Paste" mechanism that results in gene change is considered mutation: http://users.rcn.com/jkimball.ma.ult...ansposons.html Biology textbooks and websites agree that mutation plays an important role in evolution. For example, a Tulane University evolution class website notes that "the major role of mutation in evolution is the introduction of new gene variants into a population": http://www.tulane.edu/~eeob/Courses/...ng_sp2000.html 4. Your contention that "extra genes/alleles have additional effects" contradicts your favorite plant example that Coffea arabica with 44 chromosomes is more disease susceptible than C. canephora with just 22, yet you will not even address the discrepancy when asked. I took college courses in biology, botany, plant breeding and genetics and have read a lot on evolution, including college biology and botany textbooks, science teaching journals like American Biology Teacher, noncreationist evolution websites, and the U.S. National Academy of Science's book, Teaching About Evolution and the Nature of Science (1998) which can be read online for free: http://www.nap.edu/books/0309063647/html/index.html The 1994 college biology text by John Kimball is available online for free and I find it a good introductory source for evolution and biology information: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/ Many other college botany and biology textbooks have websites that provide some free information, e.g. Biology of Plants by Raven, Evert and Eichorn: http://www.whfreeman.com/raven/index.htm What have been your sources of information on evolution and plant biology? Any reasonable person can see that your personal attacks on me indicate that you have no scientific facts or arguments to back your claims. If science was on your side, it would be very easy for you to support your case with facts from books or websites. David R. Hershey "P van Rijckevorsel" wrote in message ... Dear David, I note you feel you are occupied "just pointing out [my] errors". Although I would readily admit any errors I might have made it would seem I cannot see you actually pointing out any. If I have to describe what it is you are doing it would seem you fasten upon I word I use, you connect this with a random word you derive from an unknown source and off you go ... Since you were kind enough to provide such a clear example I will use that to set the record straight. I stated: "It is like expressing human progress over the last millenia by measuring individual body weight: this may be be useful data but presents only a small part of the picture". If one were to conduct a poll as to what constitutes "human progress over the last millenia" one might get quite different answers, such as the invention of the wheel, the agricultural revolution, the invention of the printing press, the industrial revolution, instant coffee, automobiles, computers, cell-phones, nintendo, etc but genetic change would not be high on the list, perhaps not even in the top thousand. Yet you blithely state "Measuring a change in allele frequency is not at all like "measuring individual body weight" as you suggest. Human body weight is largely a function of environment, not genetics." Although I am sure you will take this the wrong way, I feel honor bound to advise you, with all due respect, to confer with your doctor about your medication. As to gene expression it is clear you are hampered by some severe misconceptions. The safe advice would be for you to refrain from commenting on this topic. This is the more so since it would not be enough for you to read a book on the topic. As I am sure you are aware re-education is much harder than education. You would need to take a course on the topic to straighten matters out, and this might come hard. You had better avoid it. Sorry to be so blunt. sincerely, PvR |
#5
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Isolated facts in biology/botany texts
I agree that mutation is not the only source of variation that can
lead to evolution but it certainly is a very important source. Even in your example of horizontal gene flow from bacteria to humans, it is likely that some of those genes and alleles arose via mutation prior to the horizontal transfer. The leading proponent of horizontal transfer, Carl Woese of the University of Illinois, believes that three cell types, bacteria, eukaryote and archaea, arose independently and underwent a lot of horizontal transfers early in evolution: http://www.usatoday.com/news/healths...-evolution.htm Even with three independent origins of cells, there would have been little genetic variation to begin with. Thus, wouldn't the greater part of the huge number of genes and alleles present today have arisen by mutation over the 3-4 billion years after the origin of life? David R. Hershey "John Margetts" wrote in message ... The human genome project has shown that some human genes originated in bacteria and have been passed to humans from the bacteria by horizontal transfer. There is no reason to believe that this is unique to humans and has almost certainly happened to many other organisms in other kingdoms as well as humans. This is evolutionary, but does not involve the mutation of any alleles, merely the addition of new (for that organism) alleles. I am not, of course, saying that mutations do not happen, just that there are other ways for the genome of any organism to change possibly leading to selection and thus evolution. John "Don't ask me what I think of you, I might not give the answer you want me to, Oh well." - Peter Green "David Hershey" wrote in message om... If chance mutations don't give rise to new alleles in plant species, then how do they arise? Many alleles do not code for "normal" or functional proteins. The explanation is that the abnormal alleles arose via mutations in the existing normal allele. snip |
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