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Microevolution in Action Lab – TA GuideThe goal of this lab is to give students the opportunity to observe the effects of two mechanisms of microevolution – genetic drift and natural selection – on allele frequencies. The simulations we’ll use obviously have MANY limitations in terms of their ability to reflect real situations, but they serve their purpose. We’ll cover microevolution in class the week before this lab runs, so the students should be familiar with the concepts. The only things that we don’t cover in class are the concept of a gene pool (it comes up in one of the videos, but we don’t discuss it directly), and calculating allele frequencies.IMPORTANT: We’ll send you access information for the SimBio Genetic Drift and Bottlenecked Ferrets simulation. You need to download the program and go through the simulation (see student instructions) BEFORE lab meeting on Friday so that you know if you have questions! If you have trouble accessing the program, contact Nat ASAP.Lab DiscussionI.Pre-lab quiz (6 points) = ~10 minChoose ~3 to 4 questions from those provided below for a total of 6 points. As usual, don’t write your own; suggestions are welcome. Obviously, some questions CANNOT be used together.What TWO mechanisms of microevolution are you focusing on in lab today?natural selection and genetic driftChoose ONE of the mechanisms of microevolution that you’re exploring in lab today, and briefly explain how it causes change in the allele frequencies of a population.natural selection: favors alleles that are beneficial in the current environmentgenetic drift: change due to random chance; random sampling; sampling error; random eventsIn a sentence or phrase, describe the difference between natural selection and genetic drift.natural selection favors traits (genes, alleles) that are beneficial for organisms (in their current environment), while genetic drift is change due to random chanceIn a diploid plant species, flower color is influenced by a gene that produces flower pigment. The red (R) allele results in red pigment, while the yellow (r) allele has the information to produce yellow pigment. A population of flowers has twenty-five individuals. Five individuals are homozygous for the red allele, ten are heterozygotes, and ten individuals are homozygous for the yellow allele. How many TOTAL flower pigment alleles are there in the population? 50 Mix up the traits, population sizes, and/or #’s of individuals. Just keep the math EASY!In a sentence or phrase, describe how you calculate the frequency of an allele in a population.total number of that allele divided by total number of alleles for that gene in the populationFor a population of 50 humans, what is the total number of alleles present in the population for a particular gene?100 (individuals only have two alleles for each gene!)In one sentence or phrase, explain why small population sizes are a concern for conservationists working to preserve endangered species.limited genetic diversity (variation); not many different alleles; limited ability to evolve by natural selection if environment changes (disease strikes); more likely to be killed off by a disease because of limited genetic diversityBeak size in the finch populations studied by the Grants changed over time as variations in rainfall amounts caused differences in the seeds the birds rely on for food. This is an example of what mechanism of evolutionary change?natural selectionII.Introduction & Overview = ~10 minASK them what they’re doing todayexploring two different mechanisms of microevolution – genetic drift and natural selectionreview/describe genetic drift [make them tell you!]changes due to random chancerandom fertilizationrandom sampling of individuals that survive a disaster (bottleneck) or start new population (founder effect)small populations are more likely to be significantly affected by genetic drift vs. large populationsformation of smaller population can decrease genetic diversity – can be further decreased by driftASK why genetic diversity is important [better able to respond to/survive environmental changes; natural selection can only act on genetic diversity that’s there] review/describe natural selection [make them tell you!]favors alleles that are beneficial for survival and/or reproduction in current environmentwhich alleles are favored can change if environment changestwo simulations to explore natural selection and genetic driftferret simulation – use what learn/know about genetic drift to design conservation strategyfinch game – explore how environmental changes can influence natural selection’s effects on a population review/describe natural selectionIII.Black-Footed Ferret Simulation = ~1 1/2 hrs. [set a time limit; let them know when it’s nearing the end]emphasize that studying evolution in real populations is challenging – simulations are often used to model changes & make predictionsbriefly remind them of the ferret scenario [or ASK them – it’s in their handout]bottleneck due to loss of main food source (prairie dogs), habitat loss, and diseasespecies declared extinct – then small population foundgive everyone a few minutes to READ the top part of the simulation instructionsemphasize that they need to READ ALL of a particular step before they start doing things (e.g. all of #1, all of #2, etc.) AND any associated questions before they start doing stuff [this is important!!]will need to record data, answer questions, stop simulation at specific point, etc.need to know what they need to do before they dive inmention the prize for the best habitat design [guessing someone will ask about this if they read the handout]emphasize that they need to:READ carefully – and read all parts of a step before starting stuff!ANSWER the lab handout questions – work in groups of two, but each person turns in OWN workASK if they have questionspass out lab questions handout [one for each student; they need their own because they’ll have their own results for the bird game]let them do the simulation and CIRCULATE to help them out!keep an eye on everyone to check their timing – force speedy groups to slow down and think!if groups finish early, they can work on perfecting their habitatswhen groups start making preserves, remind them that genetic drift typically decreases variation in small populations!! give people a heads up when it’s coming near the end of the time limitWHEN TIME IS UP (or everyone is done):have groups share average S allele frequencies and average heterozygosities – write them in a table on the boardgive prizes to group that kept the S allele frequency closest to 0.5 AND had the highest heterozygosityif no one group meets both criteria pick the one with the highest heterozygosity or have your section vote on the best oneIV.Finch Natural Selection Game = ~1 hr.NOTE: Students are NOT going to get printed instructions for this part of the lab; you will. It’s your job to lead them through the activity so please make sure you know what you’re doing! TELL THEM TO BE CAREFUL WITH THE MATERIALS (i.e. don’t spill them all over the floor!).divide students into groups of three (two if necessary, but NOT four)give each group a set of the three different beaks – students in group can decide who gets which onetell them that we’re assuming beak size is determined by one gene with two different allelesdescribe beak phenotypes/genotypestongs = big beak, BBlarge tweezers = medium beak, Bb (heterozygous)small tweezers = small beak, bbASK what pattern of inheritance [incomplete dominance: heterozygotes have intermediate phenotype]write the total number of each beak phenotype and genotype on the boardcalculate starting allele frequency of populationASK them how to do this first!do the calculations – total # B alleles/total # alleles; total # b alleles/total # alleleswrite starting allele frequencies on the boardthree different types of foodshazelnut = big seeds; corn = medium seeds; rice = small seedsdifferent caloric values [have students look at the values given in lab questions table]need certain amount of calories just to survive additional calories to contribute ONE allele (gamete) to future generationemphasize that:we’re NOT looking at sexual selection – who mates with who doesn’t matterwe’re ONLY looking gene pool of next generation (which alleles go to next generation) – we’re NOT going to determine how the alleles are “paired up” to produce offspringemphasize that same gene pool could reflect different phenotype distributionsextreme example = 50/50 allele frequencies could be all heterozygotes (medium beaks), or could be half homozygous BB (big beaks) and half homozygous bb (small beaks)other phenotype proportions are possibleASK each beak type (i.e. students with particular beak size) what allele(s) they can pass onBB = only B, bb = only b, Bb = either B or bheterozygotes – flip coin to determine which allele pass on for each allele able pass onavailability and relative amount of each food type varies with amount of rainfallwill run game under three different rainfall conditions – average, wet, and dryrulestray = area you live in with food available under certain environmental conditionscup = stomachONE piece of food at a time from tray to cup using “beak”if something falls on the bench top, you must put back on tray before grabbing again to put in stomachCANNOT also pick up non-food stuff (e.g. toothpicks; rocks)“year” will run for 1 minaverage rainfall runhave students fill their tray with the average rainfall year stuffstart timer for 1 min and tell them to go!when they’re done, have students to dump “stomach” contents on bench and fill out lab questions, tables, etc. to calculate how many total calories obtainedsubtract amount needed to survive, 25 caloriesdivide the remaining calories by amount needed per allele – round to nearest whole numbermake sure heterozygotes flip a coin for each allelemake a table on the board to collect datacollect section data and calculate new allele frequencybriefly discuss if/how changedrepeat for low and high rainfall runswrap-upgive them a few minutes to discuss the last question for the game in their handout in groups and write down their answersask for a couple of groups to share their conclusionsMake sure you collect their assignments before they leave! ................
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