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Thread: artificial selection experiment?

  1. #1 artificial selection experiment? 
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    Hi everyone. Just recently I've acquired an interest in science thanks to the likes of Carl Sagan, Richard dawkins, Michio kaku ect and have been struck with a particular fondness towards evolution and have decided to try a little experiment i.e to try and observe adaptation manifest itself in one way or another directly in the most practical way possible.Since I'm essentially scientifically dyslexic i was hoping i could get some suggestions on the best way to go about it, Also I'd be more than happy to post photos documenting progress if any one was interested.

    anyway I've composed a somewhat vague list of questions and they are

    Choice of organism - preferably something with a fast reproduction rate, Indigenous to Australia and easily visible to the naked eye

    Experiment model

    Suggested measurements to take before, during and after etc

    Basically something along the lines of this
    Artificial selection in the lab

    My daughter seems interested and i thought it might make for a good hobby
    anyways so let me know what you's think


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  3. #2  
    Universal Mind John Galt's Avatar
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    By far and away the 'creature' of choice for lab based evolutionary studies seems to be Drosophilia, the fruitfly. I believe coloniesof these with specific genetic character can be purchased, but I have no idea where. since you are new here, be aware this is not in my area of expertise and so view this as a recommendation to consider, but not act on without serious confirmation from someone who knows.


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  4. #3  
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    Quote Originally Posted by charlesdawkins View Post
    Hi everyone. Just recently I've acquired an interest in science thanks to the likes of Carl Sagan, Richard dawkins, Michio kaku ect and have been struck with a particular fondness towards evolution and have decided to try a little experiment i.e to try and observe adaptation manifest itself in one way or another directly in the most practical way possible.Since I'm essentially scientifically dyslexic i was hoping i could get some suggestions on the best way to go about it, Also I'd be more than happy to post photos documenting progress if any one was interested.

    anyway I've composed a somewhat vague list of questions and they are

    Choice of organism - preferably something with a fast reproduction rate, Indigenous to Australia and easily visible to the naked eye

    Experiment model

    Suggested measurements to take before, during and after etc

    Basically something along the lines of this
    Artificial selection in the lab

    My daughter seems interested and i thought it might make for a good hobby
    anyways so let me know what you's think
    Hello,

    Good to hear that you've become interested in Science and in Evolution in particular. Well, I have one suggestion of a clear way to observe selection in action, however it requires some reagents that you may not have access to.

    Take two vials of identical bacteria. Leave one vial alone (control). Transform the second vial of bacteria with a plasmid encoding a fluorescent protein just upstream of a gene encoding a protein that confers resistance to an antibiotic. Mix the two vials of bacteria together and plate out on antibiotic-containing plates. Only those bacteria that have been transformed with the plasmid will survive (detectable by their fluorescence).

    This would, at least, indicate selection.

    Tri~

    P.S. A variation on this, requiring access to a sequencing machine: Sequence the entire genome of the bacteria. Plate out on antibiotic-containing plates. Sequence the whole genome of any surviving bacteria.
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  5. #4  
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    Why the control? They are undetectable right?
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    Quote Originally Posted by seignet View Post
    Why the control? They are undetectable right?
    Yes, the point of the control is to prove that it is the presence of the resistance-conferring plasmid that provides the surviving bacteria with a selective advantage. Thanks for pointing out this logical fallacy though, perhaps it would be a better idea to modify the experimental design - transform the control bacteria with a plasmid encoding a fluorescent protein (obviously, of different fluorophore to the antiobiotic resistance-associated fluorescent protein). This way, it will be possible to observe any surviving control bacteria (although we would, of course, expect none).
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  7. #6  
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    Thanks tridimity for your comment but since I intend on having my 6 year old daughter participate I was hoping for something a little more apparent say along the lines of, the butterfly changed it's color/habits to avoid being eaten. Regardless of that I'd like to ask you some questions. You said
    plasmid encoding a fluorescent protein just upstream of a gene encoding a protein that confers resistance to an antibiotic.
    now since I'm new to all this I have no knowledge in molecular biology what so-ever so bear with me, but as best as i understand (just started reading The selfish gene) DNA's constitute molecules are proteins and enzymes and the collaboration of these molecules make up genes, genes that express themselves in a variety of ways fluorescent organisms for example but you said there was a PROTEIN for the fluorescent attribute and one for the resistance of antibiotics. I though that would be the role of genes or have I completely misunderstood something here?
    also what do you mean by upstream is it that on the plasmids DNA strain there would be the fluorescent protein adjacent to the resistant protein and that the plasmid would be both fluorescent and resistant to antibiotics?
    any other ideas for an experiment?
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  8. #7  
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    To understand the definition of a gene, it helps to be familiar with the central dogma of molecular biology, which essentially states that: DNA makes RNA makes protein. This is a simplification, since in reality some genes encode RNA that has regulatory functions rather than mRNA; also, retroviruses are able to reverse the direction of information flow, from RNA to DNA).

    The definition of a gene is contentious, but for the purposes of this thread we can use the following definition:

    A gene is a section of DNA that encodes for a protein.

    The DNA is transcribed into messenger RNA (mRNA) by the enzyme RNA polymerase. The mRNA is then translated into a protein on ribosomes.

    The central dogma of molecular biology is explained in this Wikipedia article: Central dogma of molecular biology - Wikipedia, the free encyclopedia


    With reagrds the plasmid I was referring to, you are right in that it is the role of the respective genes to encode the fluorescent protein and the antibiotic resistance-conferring protein. The plasmid is essentially a circular piece of DNA, like this:

    pcDNA.jpg

    Restriction digestion enzymes can be used to cut the DNA at specific sites and cDNAs encoding the protein of interest (fluorescence and resistance proteins) can be ligated in.

    What I mean by upstream - DNA has a directionailty. RNA polymerase transcribes in the 5 prime (5') to 3 prime (3') direction. Hence, anything (e.g. the fluorescence gene) closer to the 5' end is said to be 'upstream' of anything (.e.g resistance gene) closer to the 3' end. Also - since both genes are encoded on the same plasmid (on a bicistronic mRNA) you can be sure that they are co-expressed i.e. wherever you see the fluorescence protein, you can be sure that the resistance gene was also expressed.


    The plasmid can then be forced to enter the bacterial cells using a well-defined transformation protocol.

    e.g. thaw competent bacteria on ice (stored at -80*C). Pipette optimum amount of plasmid DNA (encoding the resistance and fluorescence genes) into tube of bacteria. Flick to mix. Incubate on ice for 10-15 minutes. Drop into the heat block at 42*C for 30 seconds (makes holes in the bacterial membrane, so that the DNA can enter the cells). Put the bacteria back on ice for 2 minutes (holes close). Using aseptic technique, pipette a sufficient volume of SOC outgrowth media into the tube of transformed bacteria. Incubate the bacteria at 37*C for 1.5 hours. Plate out under aseptic conditions (onto plates containing antibiotic). Any resulting colonies will be fluorescent and contain the resistance gene.

    If you have any further questions, please let us know.

    Best wishes,

    Tridimity

    Ref.

    DNA DNA - Wikipedia, the free encyclopedia
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    In terms of designing an artificial selection experiment - you could try to recapitulate the peppered moth selection. However, it would be logistically difficult - it would require establishing a habitat for them, ensuring that the population stayed in the habitat and introducing predation in a controlled way (this might also upset your daughter, to see moths being eaten!)

    Perhaps we could find something involving less emotive species, e.g. plant species?
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  11. #10  
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    For a 6-year-old I suggest guppies. They reproduce in even the most indifferently managed aquarium. Any random dozen from the pet shop will have different markings...
    A pong by any other name is still a pong. -williampinn
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  12. #11  
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    I see, it appears i had it all wrong thanks for the informative post.I do have another question though if plasmids have the capacity to penetrate bacteria giving them the attributes they themselves possess.Then in the case of our experiment wouldn't we just be exhibiting the fact that fluorescent, antibiotic resistant bacteria are indeed fluorescent and resistant to antibiotics? what I'm trying to say is that if you've made the bacteria resistant to antibiotics then they never really faced any peril and there was no selection
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  13. #12  
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    Quote Originally Posted by charlesdawkins View Post
    I see, it appears i had it all wrong thanks for the informative post.I do have another question though if plasmids have the capacity to penetrate bacteria giving them the attributes they themselves possess.Then in the case of our experiment wouldn't we just be exhibiting the fact that fluorescent, antibiotic resistant bacteria are indeed fluorescent and resistant to antibiotics? what I'm trying to say is that if you've made the bacteria resistant to antibiotics then they never really faced any peril and there was no selection
    As a population, the mixed control and antibiotic-resistant bacteria could be seen to be undergoing a kind of crude selection, since only those possessing the correct plasmid will survive when plated onto antibiotic-spiked plates. Okay, I agree that the outcome is obvious and fairly unimpressive. If you wanted to perform a 'look see' (discovery) sort of experiment, that would be possible (i.e. choose a few species and let Nature take its course). However, this would be much more difficult than performing a well-defined, hypothesis-driven experiment as above.

    Alternatively, you could take bacteria that are ordinarily resistant to a given antiobiotic and create a few different mutant strains by site-directed mutagenesis in the coding region of the antibiotic resistance gene. And then plate out on antibiotic plates. This way, it's not an obvious all-or-none situation; some of the mutants may be better protected than wild type controls (unlikely); other mutants may have a mild phenotype; and, some mutants might lose their protective effect altogether and prove non-viable. This experiment would at least involve selection that is more obviously based on the genotype of the organism.
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